Ange Postecoglou is in the midst of the biggest job an Australian coach has held in men's club football.

Postecoglou changed the landscape of the game in Australia and left a legacy in Japan, where he conquered the J1 League with Yokohama F.Marinos before he was lured to Glasgow by a wounded Scottish powerhouse Celtic, dethroned by bitter rivals Rangers.

After some initial backlash, Postecoglou has Celtic fans dreaming of glory through an emphasis on a high-octane style of attacking football and unrelenting belief in his philosophy.

But to get a clear picture of Postecoglou – the most decorated coach in Australian football – and his journey to Parkhead, you have to go back to his days at boyhood club South Melbourne.

Most know about Postecoglou's love for South Melbourne, where his passion for the sport grew alongside his father after immigrating from Greece.

Postecoglou went from juniors to seniors, winning two titles as a player before delivering back-to-back NSL titles as a coach and an unprecedented spot alongside Manchester United at the 2000 Club World Cup in Brazil.

Michael Petersen saw the making of Postecoglou unfold before his eyes. The former South Melbourne and Australia midfielder had been involved with the Australian great since around the age of 10 – the pair initially clashing in a junior rivalry between South and Port Melbourne.

Petersen eventually joined Postecoglou at South Melbourne in the late 1980s.

"He was a natural leader," Petersen told Stats Perform. "In a lot of ways, probably needed to get up to speed personally, but it was an invisible leadership. But he was always serious about his football. He loved the club. So his loyalty was unquestioned."

A trail-blazing coach, Postecoglou's career in the dugout is well-documented but he was also successful on the pitch – the former defender is considered to be one of South Melbourne's greatest players, having won eight pieces of silverware, while earning four international caps for Australia.

However, Postecoglou's career was cut short due to a knee injury.

"He was underestimated [as a player] but obviously he got wiped out pretty young at 27," Petersen said. "I think you're just coming into your professional career [at that age]. At the time, South Melbourne had a lot of good players in all the lines so he probably went a little bit unnoticed but not in our changing room. He was very well respected. You obviously don't make someone captain if you're not first on the teamsheet, so he was always first picked on the teamsheet."

Postecoglou's success has been shaped by his father, Dimitris, and legendary Hungarian Ferenc Puskas.

The 56-year-old played under Puskas from 1989 to 1992, forming a close bond, before launching his own coaching career at South Melbourne.

Postecoglou was appointed in 1996 and former general manager Peter Filopoulos was instrumental in the ex-captain's rise from skipper to coach.

"Every time I spoke to Ange, I felt like I was educated about football. Because I was an administrator. I never played at the high level. I was a little bit more educated about South Melbourne's history and he was very proud of South Melbourne history, the club and he always had these really big aspirations for the club, but also big aspirations for football in Australia as he still does," Filopoulos said.

Postecoglou's transition from player to senior coach at South Melbourne almost did not happen following the sacking of former Socceroos boss Frank Arok.

After a 3-0 loss away to Marconi in March 1996, Arok was relieved of his duties and Postecoglou put in charge on an interim basis for the remaining three games of the season.

"I remember getting the long bus trip to the airport from Fairfield and Frank had slumped in his chair and was just sulking a little bit. The players started to misbehave and were bantering. It was as if they had won 3-0, not lost 3-0. I could see Ange to the right of me was just not amused at all right, I'm sitting at the front of the bus as the official. And it got to the stage that it was out of control on the bus," Filopoulos recalled. "He went up to the front of the bus and picked up the microphone. He said, 'You listen to me, you blokes'. It was silent and he said to them, 'I've played for this club from under eights, right through to every level of South Melbourne, I've worn this jersey for every team age group, to the seniors, I captained this club and won championships. If you want to muck around, no problem, we lost 3-0 but I just want to tell you my perspective, today was the worst performance I've seen of any, any South Melbourne team of any age group in my entire career. So if you guys are happy with yourselves, and you want muck around on the bus, why don't you just reflect on the disgraceful performance and how you disgraced the team jersey today and the club'.

"That was it. There was silence for the rest of the bus trip. And then we got to the airport. And there was all these shuffling of the boarding passes. No one wanted to sit next to Ange. Hindsight is a beautiful thing, right? But I remember thinking to myself back then this guy has something special."

However, Postecoglou – who was working in a bank at the time to supplement his salary of being an assistant coach – was not even in the equation to make the step up permanently after winning all three games as South Melbourne's hierarchy eyed bigger and more established names.

"I'd be in the board meetings as a general manager, and they'd be speaking about Zoran Matic and [former Australia coach] Raul Blanco, all those big names of the time. Ange came into the office and he wasn't really mentioned around the table. They all thought he'd automatically be an assistant," Filopoulos said.

"He goes to me what's going on with the coaching gig? And me naively, I said we had a meeting last night and we're talking about Matic and Blanco. And Ange goes, 'What about me big fella?' I said, 'Are you interested?' He said 'Yes I am, I am interested'. I said, 'Well Ange, if you're interested, you need to make it known'. I thought, I wonder what the young fellas thought. We had the younger committee members and older ones. I remember ringing up some committee members and I threw Ange's name in the mix and over a few conversations, you have to give him a chance to present.

"So what I did back then, we were a very close-knit social group, the younger guys and I set up a barbecue at my place. The coaching conversation came up. And everyone's talking about those big names again. And then Ange said, 'You know I'm interested right?' And someone said, 'What? Are you really interested?' Ange started talking about his philosophy and ideas. It went for like 30 minutes. It was like a full-on pitch without knowing it was a pitch. He finished and it was dead silence. The vice-president at the time said 'Ange you're our f****** coach mate'. That was it. We lobbied hard and got him through. It was tough to get it through. There were some really older guys who weren't convinced.

"Ange got the job. And a lot of people would say that was a foresight. I would say, sometimes it was instinctive that it was the right decision. He changed everything. So there's me as general manager, it was actually quite good, because there was all these expectations and all these different things he wanted in place, which meant I worked pretty hard for him to deliver it."

But it was not all smooth sailing after fighting tooth and nail to appoint Postecoglou – a run of just one win from seven games to open the 1996-97 season had some South Melbourne committee members calling for Ange's head.

Filopoulos said: "There were a few phone calls from committee members and I remember one guy, he said 'you need to get rid of him at midnight tonight so no one sees him leave the club because you've made a mistake, and because you orchestrated all of this, you can follow him behind'.

"It came down to the eighth game at Marconi for a coach's career, really, because the pressure was on. We won after a scrappy 87th-minute goal. Had we not won that game, it would have been a different future for Ange. The rest is history. After that, he improved our football club. He took it to another level. We became a true destination club."

"So a similar story to Celtic, it takes some time, right? Because he does, on my experience, he turned our program upside down. He has meticulous detail and thought process, even to the point of dressing room access," he added.

Petersen, who also served as Postecoglou's assistant during his tenure as head coach of the Young Socceroos, experienced the "seamless" transition from player to coach up close and personal.

"There's layers to having a good football IQ. There's layers to it," said Petersen, who was told his playing career was ending by Postecoglou. "Ange has always had it. No, not even an issue. Very, very astute. I can rubber stamp that from, from way, way back. And that's to a point is if you love something, you really go deep into it. He goes deep into, you know, picking a football team for any matchday is a bit of a puzzle. You've just got to put the whole thing together, you've got to get the right balance of energy, skill sets. Who's going to actually perform on the day for that given day?

"He doesn't get it wrong a lot. And I can say that, but I think his history shows it. He's managed to get it right on the big days. It's by design, it's not coincidence. He gets it right. You can read all the books in the world. And you either got that gift, or you don't have that gift."

"At the time [after coaching South Melbourne to NSL glory] I thought Ange was Australia’s modern-day version of Alex Ferguson," he continued. "To this day I haven't changed my mind as I have watched him evolve and succeed and continually challenge himself and the type of football his team produces. Ange wins and wins well with style and grace."

From South Melbourne to Australia and Japan, Postecoglou has won it all – a pair of National Soccer League championships, back-to-back A-League titles, a record 36-match unbeaten streak at Brisbane Roar, plus a ground-breaking 2015 Asian Cup triumph with the Socceroos and a J1 League crown with F.Marinos – while silencing his doubters.

Postecoglou, like Manchester City's Pep Guardiola and former Juventus and Chelsea boss Maurizio Sarri, pushes the boundaries. Firmly set in his belief of how football should be played, Postecoglou's approach never wavers and success follows in his pursuit of excellence.

That has always been the case for Postecoglou.

Recalling Postecoglou's first steps in senior coaching and his pitch-side antics, Petersen – who also worked alongside Ange at South Melbourne after retirement – said: "We almost had a rule, no one was allowed to talk on the bench. If you're gonna say something, it's gotta mean something, otherwise chitter chatter and joking around, none of that. So there's none of this micro-coaching, if you like. Ange was almost locked in tune with the game. He was actually very, very still, quiet and measured."

Postecoglou is known for not getting too close to his players and Petersen added: "I think that's a maturity beyond his years in a sense that he always, because he probably had to start coaching young and he kind of realised early that you do have to draw a line from mateship because players are insecure creatures, and they'll look for any way to get a way in and if you can be pals, you might jag a spot because he likes you.

"Ange never did that. He made decisions that were based on what was best for the club, not necessarily on the individual. Even as a captain, looking back, he was galvanising the hierarchy, the directors of the football club, everything was all about what was best for the football club. I think that's rare to see players who do that. And then already when they transition into assistant coach and then senior coach, you knew there was a line. And that was all right. I think, in the wash-up, once you know the rules of a gaffer, you love it, you go, 'Okay, well, I know where I stand, I've got to perform'. And it's not just performing in games, it's performing at training. We have to perform, every training session means something.

"We joke around in the changing rooms and then we had fun. We had ghetto blasters, telling jokes. I think the moment we hit the football pitch, for that block of time, for an hour and a half, it was business. There's no laughing, football is serious. Because you laugh and joke, you lose football games. So you train how you play. So the intensity should always be at training. I think Ange knew that already at a young age – perform at training, transition that into games, and then whatever happens after hours, yeah, let's have some fun as well."

"The biggest trouble with Celtic is trying to keep hold of Ange. In three or four years, you're going to have the same situation. He has won multiple titles and he will be trying to get a move to England or one of the big leagues. That is his pathway."

Ange Postecoglou is cut from the same cloth as Pep Guardiola and Maurizio Sarri – an emphasis on a high-octane style of attacking football, with an unrelenting belief in their philosophy.

But his appointment as Celtic manager has caused a stir in Scotland. Fans have questioned his ability and credibility to make the step from Asian to European football.

Postecoglou has been tasked with leading an embattled Celtic back to the Scottish summit after the Bhoys were dethroned by bitter rivals Rangers in 2020-21.

There are some parallels to legendary manager Arsene Wenger. Like Postecoglou, the Frenchman had history in Japan, having spent a year with Nagoya Grampus before being brought to the UK by Arsenal in 1996.

Social media was not around at the time of Wenger's Gunners arrival, though it would be safe to assume he would have been subjected to similar criticism from a supporter base desperate to wrestle the trophy back to Celtic Park.

Those questioning Postecoglou's pedigree should look no further than his CV – the most decorated coach in Australian football history, having also transcended and changed the landscape of the sport Down Under.

From South Melbourne to Australia and Japan, Postecoglou has won it all – a pair of National Soccer League championships, back-to-back A-League titles, a record 36-match unbeaten streak at Brisbane Roar, plus a ground-breaking 2015 Asian Cup triumph with the Socceroos and a J1 League crown with Yokohama F.Marinos, while silencing his doubters.

A former Australia international, Postecoglou – who delivered two NSL trophies within three years of his tenure in charge of boyhood club South Melbourne – truly announced himself at the helm of 'Roarcelona'.

After a brief and unsuccessful stint in Greece in 2008, followed by a short spell in the semi-professional state league in Victoria which resulted in relegation, Postecoglou landed in Brisbane the following year.

Postecoglou oversaw a rebuild and after asking to be judged a year from the time he replaced ex-Socceroos boss Frank Farina, his project culminated in the development of arguably the greatest footballing side in the history of Australian football.

Playing an entertaining and possession-based brand of football, the Roar won the championship in 2010-11 and successfully defended their trophy the following season amid a 36-game unbeaten streak – an all-time Australian football code record for the longest undefeated run, surpassing rugby league outfit Eastern Suburbs' record set 74 years prior.

Postecoglou also coached Melbourne Victory before his Australia appointment in 2013. In the A-League, his teams scored 1.7 goals per game; only one head coach (minimum 30 games) has a higher average in the competition's history (Graham Arnold - 1.8).

The Greek-born boss left Australia's domestic competition with a 51 per cent win percentage as head coach – the joint-fifth best of any manager in the competition's history.

Erik Paartalu was one of Postecoglou's first signings as Roar coach and the ex-Australia international told Stats Perform: "He will be absolutely buzzing. He isn't the type to take a job on lightly. He would've researched beforehand. I'm sure he's probably been offered jobs of this calibre before but wasn't ready.

"Ange has always been ambitious. This guy just doesn't stop. Any other Australian coach that would've won the J.League would've just stopped there and chilled out in Asia. The guy is in his mid-50s. He would've researched this whole situation at Celtic, who is leaving and who is coming, who can I get in? I know he's already thought about his next step from here."

"With Ange, it was the tactical side of it where he explained and broke things down so easily on the pitch, whether that be playing 11-v-seven, so you would have a huge overload and confidence in possession. Or if it was in a video session, always pointing out the good things about people," said Paartalu as he reflected on his Roar days. "He always pumped up the smaller details of the team. His way to getting us to feel, you just felt so confident."

Postecoglou, like Manchester City's Guardiola and former Chelsea and Juventus boss Sarri, pushes the boundaries. Firmly set in his belief of how football should be played, Postecoglou's approach never waivers and success follows the 55-year-old in his pursuit of excellence.

"That's what we loved about him," Postecoglou said. "We went on that unbeaten streak and then lost five in a row. Never even mentioned getting close to the record. It was just like 'if we play the way we play, we'll wipe this team off the park'.

"In the first grand final [2011 against Central Coast Mariners], the goal I scored in the last couple of seconds [of extra time, 120th minute to force penalties after 2-2 draw], it was the build-up before that showed everything that we're about. [Michael] Theo had the ball and could've gone long, but he throws it to [Massimo] Murdocca and we build up from the back and get a corner. That was so typical of the way he wanted us to play. Even in training, it was like, 'don't put the ball above waist height or in the air'. If you did that, you had to give the ball to the other team. So we were drilled into knowing short passes, through lines, everyone in the right position, movement off the ball, entry points on the edge of the box, guys overlapping, 4-3-3 and don't cross the ball in if you're not sure. That was his blueprint. We were going to play his way all the way to the death. When we lost five in a row, he never got angry. He was so clear, saying keep doing it, be confident, keeping passing the ball.

"He definitely improves players' game intelligence when they work under him. You feel 10-feet tall and just know your job inside and out because of the way he prepares you."

Handpicked to introduce style and substance to the Socceroos in 2013, Postecoglou led Australia at the 2014 World Cup. Undaunted by the 'Group of Death', Australia left Brazil emptyhanded, but took it to Chile, the Netherlands and holders Spain in stunning fashion.

Postecoglou delivered a first Asian Cup to Australia in 2015, while he secured qualification for the 2018 World Cup before stepping down prior to the Russian showpiece.

The Socceroos scored 86 goals in A-Internationals under Postecoglou – the second most they have scored under any manager since the beginning of 1965 (Frank Farina - 197). Australia won 22 games during his tenure; only two managers have won more since the beginning of 1965 (Frank Farina - 34 and Holger Osieck - 23).

Postecoglou eventually landed at F.Marinos – part of the City Football Group – in 2018.

Physical performance coach Gregory King was part of the team Postecoglou put together to accompany him on his journey in Japan, where he ended F.Marinos' 15-year wait for league glory in 2019.

Postecoglou left F.Marinos with the highest winning percentage (49.2 – 58 victories in 118 games) in the history of the club. Since joining the Yokohama club, only two managers have a better winning percentage than Postecoglou; Toru Oniki (65) and Go Oiwa (50) from a minimum of 10 games.

Despite the language barrier, F.Marinos bought into the Postecoglou way. Since 2018, the team ranked first for passing accuracy (86.5) and possession (63.2), while they were second for goals per game (1.9), expected goals per game (1.8), shots per game (15.2), shots on target per game (5.3), shot conversion rate (12.6), shooting accuracy (47.2), chances created per game (11.4), passes per game (619.4), passing accuracy in opposition half (82.4), big chance total per game (2.4), big chance created per game (1.8) and big chance scored per game (1.1).

"He definitely has a really good understanding from conditioning, strength and sport-science point of view," King told Stats Perform. "His attention to detail is optimal. You know you can't pull the wool over his eyes. He knows everything going on within his team but he lets you run your own department. He gives you a license to achieve the objectives of the team in your own way."

During F.Marinos' triumphant season in 2019, Postecoglou's men covered the greatest distance in the J1 League (116.48), ahead of Oita Trinita (114.79km). They also tallied the most total sprints with 191, more than FC Tokyo (174).

As Postecoglou prepares to take pre-season training with Celtic, King said: "They're definitely in for a lot of hard work. Really quality football sessions based around the principles of how he wants to play. But, there's no holding back in terms of intensity.

"I think they will enjoy the sessions, however they will be pushed physically. The football we played in Yokohama was extremely high intensity. The physical qualities have to be at their peak. We expected our best players to play regularly, so to be able to do that, the players have to have a lot of good hard work behind them and to be able to cope with it."

"I'd be very surprised if he wasn't looking closely at injury history, how many games they've been able to play over the past seasons in terms of durability. Speed is obviously a massive factor from the forwards and also the centre-backs being able to play really aggressive and a high line. You can only do so much when you have them. We feel we can improve them all physically but from a conditioning point of view, you have to recruit players strong in those areas already to be able to play the way we did."