When Diego Costa stands in front of you, it is possible to believe every story you've ever read about the upbringing that formed the footballer. When he stands and speaks politely but reluctantly before a group of journalists, he could be a 1950s prizefighter. His face is lined and bears evidence of a thousand battles while beneath his thick eyebrows - he is not a manicured footballer - his eyes are sad and hard.
Diego Costa has always felt he had no choice but to fight. Jose Mourinho said earlier this season that Costa came from a place "behind the sunset", a place Mourinho said that had given Costa values he had never lost.
Diego Costa grew up in Lagarto, a remote city in northern Brazil which he has said possessed no facilities, no football pitches with grass so he played where he could. "The street was my school," he said once.
He grew up fighting. When he was 16 Costa was given a four-month ban for punching an opponent and threatening a referee, a situation which has echoes of another footballer who never lost the influence of the streets, Luis Suarez, who head-butted a referee when he was also 16.
By that time, Costa had moved to Sao Paulo with his family when he was 14, taking the familiar journey from northern Brazil to the sixth largest metropolis in the world.
He was serving his ban when an employee of Jorge Mendes came to watch Costa's side Esportivo Capel play. For some reason, the ban was lifted and the employee of the man who would become the most influential man in world football saw something in Costa and offered him a chance to go to Europe.
For Costa, the fighting was not over but given where he had come from, perhaps the years that followed were not so difficult.
"On the pitch I fought with everyone, I couldn't control myself. I insulted everyone, I had no respect for the opposition, I thought I had to kill them," he said a few years ago of the years in Lagarto.
"Boys who grew up playing in academies are taught to control themselves and respect others, but no-one ever told me otherwise, I didn't have a school to teach me this. I was used to seeing players elbowing each other in the face and thought it was the norm."
Costa's formative years as a footballer appear to have shaped not only him but those who play with him.
Like Costa, Filipe Luis arrived at Chelsea in the summer from Atletico Madrid. He had made the same journey from Brazil to Europe but he is a different personality to Costa as he acknowledges. "I think for some players like me it is not easy when they come to a new club. They have new partners on the field, everything is new, especially the physical side. It's really different but for Diego it is never difficult, it's easy because he's a top five player."
Filipe Luis believes that Costa will shortly be considered among the top five players in the world and can win the Ballon D'Or. When Filipe Luis arrived at Atlético in 2010, Costa was already three years into his time at the club but he had been loaned for every one of them. In the time they were together, Costa improved every year.
"If you go back to the past and look where he started and how he suffered in his career, he never needed to adapt in any place," he says. "Diego always goes and scores. He doesn't care about nothing. He just wants to play and play the best he can and score goals. That mentality is really easy for him and the clubs that have him."
Yet Filipe Luis echoes Mourinho's comments about the transformation in Costa when he walks off the pitch. "He is a simple person, he has a big heart, he tries to help everybody, his friends, his family, his team-mates. Sometimes inside the field he looks like he has crazy fights but outside the field, he has one of the purest hearts I've ever known in my life."
Costa's mentality has contributed to Chelsea's start to this season and his presence has led to Mourinho's barely unspoken conviction that his side will win the Premier League this year.
Last season, Mourinho appeared to be engaged by the big games. Before Chelsea played at Anfield, he produced a virtuoso work of performance art. Last week, he was disengaged. He is said to have been dismayed by the number of FA charges he received last year but he would probably take the hit again if he felt it was required. This team don't look like they need the assistance.
They dropped points at home to Schalke on Wednesday night but Mourinho rested Costa and he will still believe Chelsea can top the group. The aftermath of the game is a reminder of Chelsea's strength as their squad head along the touchline which turns into the mixed zone. While Costa is talking, Thibaut Courtois walks by. "Speak English, man," he says to his old Atlético team-mate.
There is another reunion today when Chelsea play Manchester City at the Etihad and Costa faces one of those who stood in front of him when he was at Atlético.
"I loved watching him," Costa says of Sergio Aguero. "He is, for me, the best I saw play. The best as a team-mate. I enjoyed it a lot to play with him. For me, he's a great. He's one of the absolutely top-level forwards around. I knew when he was there, Sergio was God. You knew what a great player he was. The truth was I learned a lot with him. I hope things keep going well. Now we'll see who comes out on top."
Mourinho said at the beginning of the season that he felt Costa had already overtaken those who were ahead of him at Atlético, Aguero and Radamel Falcao. Certainly he is a footballer Jose Mourinho needs more than any other - as Wednesday demonstrated - but he must be managed because of a hamstring injury which prevents him playing three games in a week.
He will start today. Mourinho says it's a risk but the real risk would be leaving out a player who has scored seven goals in four Premier League games and has brought a physical presence to the side.
If Mourinho and Costa share some qualities, the forward is pleased about it. "I don't like to lose. It's something that many times goes well but other times goes badly for me. I'm just like that, I just always try to win, to get better, do my best and it always annoys me to lose."
Costa's ambition hasn't been dulled by the move. "He always wants to win and if he don't he gets crazy, really mad," Filipe Luis says. "That kind of person - Jose is also like this - people with ambition, they always want to win and if they don't they really get mad and they try to get better. I think these kind of people really have to succeed in life."
Costa sees this ambition as natural. "I think anyone in life, everyone in the world, no matter what work they do, they should think of wanting to get on, to win, improve. I don't think I am the type of person who thinks 'I dunno, things are getting on top of me'. But it's not that I think I think I'm any different to most people. I always make a big effort, fight with all my strength, make the best of a situation, and always want to win."
Those qualities have led to some tangles, the latest last weekend against Swansea.
"I haven't really had any physical battles," Costa says, but he has had some skirmishes including a long engagement with Seamus Coleman which Mourinho dismissed as a provocation.
Costa picked up one of his two yellow cards in that game after another tangle with Coleman which Mourinho says was a "little reaction" to Everton's aggression.
"I think the referees are there to see the provocation. Diego is trying to play. He is not afraid of aggressive opponents. He doesn't let other players intimidate him. He is there to play football and try to score goals."
This seems to be Diego Costa's solution to any problems he encounters on the field. "You've got to know how to manage these situations. The truth is I'm fairly relaxed. If they provoke me, I'll score against them."
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