Ralf Rangnick has been called a lot of things during his career in football -- Yussuf Poulsen, the RB Leipzig striker, says he's a "perfectionist," while his teammate Kevin Kampl says Rangnick is "in love with football." There were others who poked fun at him back in 1998 when he explained his then new-age tactical system "gegenpressing." But when Jurgen Klopp calls Rangnick "one of the best, if not the best German coach," you listen.

But in 2020, German coaches are the sought-after coaching commodity: take Thomas Tuchel at PSG, Klopp at Liverpool and Julian Nagelsmann at RB Leipzig. All of them were influenced or taught by Rangnick. At the start of this season, seven of the 18 Bundesliga clubs were managed by coaches who had spent time with Rangnick. His influence also spread to key personnel currently in the Premier League, Ligue 1 and Eredivisie.

When Rangnick started out in the 1970s, managers tended to have impressive playing careers and then went right into coaching. It was unfashionable to have a manager who was in the shadows of the German second tier. It was also seen as insulting to champion theories of "gegenpressing" -- a philosophy built on pressing and counter-pressing the opponent, with an emphasis on attacking with positional fluidity -- in an age where German football was rigidly 3-5-2, reliant on tried-and-true methods like man-marking that had made Germany a superpower -- three World Cups and three runners-up prior to 1990, three Euro titles and two more second-place finishes prior to 1996 spoke to their success. But Rangnick, who had a mediocre, semi-pro playing career, never gave up.

He is living proof of what Italian manager Arrigo Sacchi -- one of Rangnick's heroes, along with Valeriy Lobanovskyi and Ernst Happel -- meant when he shot back at a reporter who'd questioned his managerial credentials due to the lack of a polished pro career. "I never realised that in order to become a jockey you have to have been a horse first," Sacchi said.

As we talk over Zoom, Rangnick chuckles as he rolls Sacchi's one-liner out.

"The top coaches are not only good leaders of their team but they are also experts in the different areas of the game," Rangnick tells ESPN. "If you look at the Bundesliga, more than half of the 18 coaches have not had a significant professional career but rather started to develop their methodological skills in youth football."

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It was transfer deadline day across Europe when we spoke. He was assessing some of the players he helped nurture, like Timo Werner and Naby Keita. He was full of praise for Joshua Kimmich, whom he plucked from VFB Stuttgart's academy while at RB Leipzig, and Sadio Mane, whom he brought to RB Salzburg. These are just a handful of the players he scouted and signed in his role in charge of Red Bull's sprawling football empire.

Rangnick was one of the key catalysts behind the ascension of RB Leipzig, who went from foundation to the semifinals of the Champions League in just 11 seasons. They now sit top of the Bundesliga, and travel to Manchester United in the Champions League this week, though Leipzig and these players are just one part of his ever-developing legacy.

There's an unwavering calmness as he talks through the last year, in which a protracted move to AC Milan never materialised and he left Red Bull after eight years expanding their impressive reach. He then looks to the future and his next move: smiling and methodical, but with this inherent understanding of football and a brain that has a heatmap of disciples stretching out over Europe.

A brief history of Rangnick's coaching CV starts in 1983 after a short-lived on-field career.

"My coaching career started at the age of 19, senior football then at 25," Rangnick told ESPN. "In Germany at that time, it was almost impossible to have any role models in the first or second division who inspired me." He did not like the 3-5-2 system adopted in Germany -- the formation which incorporated a 'libero', two man-marking defenders, two defensive midfielders, two wing-backs pounding up and down the flanks and then a No.10 and a playmaker. He thought it limited, uninteresting.

"I wanted to play in a different way. Around this time, I met Helmut Gross [a hugely influential figure in removing the libero from German football but worked more as an adviser rather than head coach] who was an early mentor for me and for many other German coaches. He introduced me to the ball-orientated zone-marking technique, which was being implemented at AC Milan. We studied AC Milan hours and nights on end, and it became clear that this was the style of football I wanted to play with my teams."

This was the genesis of "gegenpressing." In 1998 he presented his tactical approach on German TV. Dressed in a black suit and matching shirt, with awkwardly brushed hair and rimless glasses, he explained his new innovative manner of counter-pressing. He was soon coined the "footballing professor," a term later used as respectful admiration, but originally met with derision and doubt.

"The reaction from the media as well as others in football was extraordinary," Rangnick said. "The main reason for this was that 30 years before, Frank Beckenbauer set the benchmark for most teams in our country when he created a libero-sweeper position for himself. Franz himself even said in the mid-90's, that you cannot play with a zone-marking back four line because German players will not understand how to play it. I asked myself why should German players be any less intelligent than those in Belgium, Spain or the Netherlands? For me that was simply not logical."

The German football system needed to collapse, before it could accept change. When the national side crashed out of Euro 2000 in the group stage, it led to a wholesale review of their system.

"Well, it's very simple," Rangnick says. "[Gegenpressing is] a very proactive style of football, similar to the way in which Borussia Dortmund and Liverpool have been playing under Klopp," Rangnick said. "We like to press high, with a very intense counter-pressure. When we have the ball, we do not like any square or back passes.

"The goalkeeper also should not be the one with the most contact on the ball. In almost every league and every country, the goalkeeper is technically the most limited football player on the pitch and therefore we have to make sure that he has the lowest contact with the feet. It is a fast, proactive, attacking, counter-attacking, counter-pressing, exciting and entertaining [style of] football."

After three years at Hannover (2001-04), where he also got them promoted to the Bundesliga, and then a season at Schalke (2004-05), it was at Hoffenheim where his coaching stock went through the roof as he led them from the third tier to the Bundesliga in 2008.

"What we did in Hoffenheim had a lot of influence on German football," Rangnick said. "I remember in our first year in the Bundesliga in 2008 we played Borussia Dortmund under Jurgen Klopp, who came from Mainz to Dortmund, and we dominated them 4-1.

"It could easily have been six or seven, because we continuously pressed them for the entire game. The following week Jurgen said that this is exactly the style of football he wants to play with Dortmund in the future. During the next two years he developed his team in such an impressive manner that they managed to win two consecutive championship titles and two cups."

Following a brief spell at Schalke in 2011, which peaked with them reaching the Champions League semifinal, he became sporting director of Red Bull's new football arm in 2012. This is arguably his greatest achievement: he challenged the established order in Germany with a new-age structure which built a worldwide network which raised the bar in player identification and recruitment.

Rangnick offered a vision anchored on youth, backed up by analysis and technological advancement with the goal of creating sustainable success on the field while making a profit through selling players at the height of their value and then replacing them with hidden gems thanks to the organisation's extensive scouting network. Eight years on, and having worn different hats ranging from sporting director to manager (he took charge of RB Leipzig in 2015-16 and then 2018-19), RB Leipzig are now perennial top four contenders in the Bundesliga, RB Salzburg have won the Austrian Bundesliga seven times on the trot and their other teams in the USA (NY Red Bulls), Red Bull Brazil and Red Bull Ghana are all evolving and developing within their system.

Leipzig are a controversial team in German football, with fans of the more traditional club arguing their business model goes against the 50+1 ownership. But they are successful.

"It is quite like in other areas of life, if you are ahead of your time with new developments and pathways, it may provoke certain reactions," Rangnick said. "Just to put things into perspective, the club was founded in 2009 and won three promotions in five years. Since 2012, it has secured its place in the top-tier Bundesliga and has continuously participated in Champions League, even making a semifinal in 2020. It is something truly rare and extraordinary."

But equally extraordinary is the Red Bull pipeline of players, as well as the long list of coaches who worked under Rangnick. At Liverpool alone, you have Keita, Mane and Takumi Minamino, while Rangnick signed Roberto Firmino to Hoffenheim and managed Joel Matip at Schalke. Rangnick feels this synergy is because Klopp and he share "similar views on football". So do a number of coaches throughout Europe.

The School of Rangnick alumni is extensive. Bayern Munich's head of youth Jochen Sauer was CEO of RB Salzburg from 2012-17. Borussia Monchengladbach's staff Marco Rose, Alexander Zickler and Rene Maric have all worked or played under Rangnick, so too Adi Hutter at Eintracht Frankfurt and Sebastian Hoeness at Hoffenheim. Then there's Markus Gisdol at 1.FC Koln, Robert Klauss at 1. FC Nurgenburg, Oliver Glasner at Wolfsburg and a host of others. Over at Monaco their sporting director Paul Mitchell is formerly of RB Leipzig, PSV Eindhoven's head coach Roger Schmidt was RB Salzburg boss from 2012-14 and Ralph Hasenhuttl was at Leipzig from 2016-18 and has been in charge of Southampton for two years. Then you have Julian Nagelsmann at RB Leipzig and Jesse Marsch at FC Red Bull Salzburg who both learnt from Rangnick.

And then there are Julian Nagelsmann and Jesse Marsch.

Nagelsmann, 33, managed Hoffenheim and then replaced Rangnick at Leipzig ahead of the 2019-20 campaign (Rangnick stepped into the manager role for a season to keep the seat warm for Nagelsmann). "Ralf has a special way of looking at football," Nagelsmann told ESPN. "I used Ralf's philosophy at Hoffenheim; counter-pressing is a very important topic."

Over at RB Salzburg is Marsch, who was assistant to Rangnick in the 2018-19 campaign at Leipzig and coached New York Red Bulls from 2015 to 2018. "The beauty of Ralf is that as intense as he is, he also gets really excited about new ideas. As traditional as he is in some ways, he is also very innovative. This is the beauty of Ralf. His contrasting mentalities and his ability to continue to grow and adjust and adapt to the younger generation -- he's got a gift," Marsch, 46, told ESPN.

Rangnick is 62 years old, but still has the thirst for another big challenge. He came close to joining AC Milan in the summer, but they opted to continue with then-interim coach Stefano Pioli.

"When they contacted me in October they were 13th in the league, just three points from the relegation zone. Then [the] corona[virus] came, after the break and restart they had 12 games and won nine of them with three draws. So it would have neither been wise for myself nor for the officials of AC Milan to change everything after such a successful period of time."

Rangnick's vision for AC Milan would have seen him have a powerful voice in both the operational, recruitment side, and then the hands-on role of coaching and picking the team. Almost like a 2020 version of Arsene Wenger's time at Arsenal. It rocked the boat. Paolo Maldini was critical of Rangnick amid the rumours over his appointment, but Rangnick is resolute in the demands he makes of prospective clubs.

As he assesses his next move, he talks about his three fundamental, non-negotiable pillars of success which he integrated into the Red Bull model.

"For me it has always been very clear, there needs to be someone in the club who is responsible for the club values and guidelines," Rangnick says. "Someone who is in charge not only for the corporate identity, but also for the corporate behaviour of the entire organization. In this context, I like to speak about three C's in football: capital or cash, concept and competence.

"It is certainly helpful in football and in business to have some money at your disposal, however, this money will not help you if you do not have the other two C's in your portfolio. In order to be sustainably successful, you need to have a plan on how to develop the club and the best possible and competent people to implement the concept and plan. Those three C's were the foundation of our [Red Bull's] sporting success paving the way for the development of players with quality and increased market value at a factor of 10 or sometimes even higher."

Player ID is integral. Rangnick educated his scouts to assess players as if through his eyes "It makes little sense to develop a scouting department or engage professionals if you do not listen to them," he says. "For me it is imperative to proactively plan your transfers and not just rely on agents recommending their players. This enabled us over the years to scout and sign players such as Marcel Sabitzer, Marcel Halstenberg, Lukas Klostermann, Dayot Upamecano, Kimmich, Mane, Keita and Kampl."

Alongside analytical and tactical evolution, he feels the next step for football is to master the player's mind.

"Top mentality is the talent of the personality and player strives to get better every single day. In addition to optimal mentality, one of the most important aspects to train in the next few years will be to develop the cognitive abilities for decision making under pressure when players are in restricted and tight areas of the pitch."

Rangnick's next step is unknown. Manchester United have long been linked with him as a potential sporting director, while he has been interviewed for previous vacancies at Everton and the England national team. He's not yet ready to look back and assess his achievements and role in 'gegenpressing' as we know it, but instead he wants to take all of this experience and knowledge and throw it into another club. There's an itch there; perhaps the Premier League, or a big Champions League-challenging side. But whoever it is, they will benefit from Rangnick's ever-evolving view on how German football should be played.

"As we have shown in the last 20 years, we can remain true to the German virtues which can be characterised as follows: disciplined, combative, and an enormous will to win in our playing style while also developing top-class strategic minded coaches who know how to play modern football.