Dark knight Costa at war with himself as well as the world
Chelsea deny that Diego Costa said "I go to war, you come with me" when he arrived for his first day at the club in the summer of 2014. But it has become legend because it always felt like he could have said it.
The story goes - and despite the denial it is still repeated by people with strong links to the club - that when Oscar introduced Costa to John Terry, Branislav Ivanovic and Nemanja Matic at Chelsea's Cobham training ground, those were the eight words of English he had prepared.
Since then Costa has not learnt much more. But he has certainly gone to war. English has not come easily to him, although he has finally started to speak it a little. And - as everyone who has dealt with Costa knows - if he does not want to do something, he will not do it.
He is one of the most headstrong, aggressive but also charismatic footballers the Premier League has known. A Jekyll and Hyde in Chelsea blue. Popular with, and respected by, his team-mates; disliked by the opposition.
Here is a man who can switch from a scowl to a smile and back again in an instant; dark and light in a second. A man who can allegedly spit into his glove and smear it down an opponent's shirt on the pitch but also refuse to train because staff at the club he was at (Albacete) were not being paid, although the players were.
Last weekend the dark side came out again. His behaviour at White Hart Lane, when he was finally dropped by Chelsea manager Jose Mourinho after his indifferent run of form, with questions over his fitness and commitment, was entirely in keeping with his character.
Not taking part in the warm-up or the post-match warm-down, coming out without his boots on and throwing a bib in the direction of Mourinho. But what has made him this way?
His behaviour at Tottenham came as no surprise to Mourinho, who has tracked Costa's career since the player arrived in Europe aged just 17 when he joined Portuguese club Braga.
Jorge Mendes, who represents both Costa and Mourinho, spotted Costa and identified him as Didier Drogba's eventual £32m replacement at Chelsea.
The problem is there is no replacement for an out-of-form Costa right now.
Chelsea's second-choice striker is Costa's former Atlético Madrid team-mate Radamel Falcao, another Mendes client, but he is injured and even Mourinho has failed to help him rediscover his mojo.
The third-choice is Loïc Rémy, who Mourinho does not appear to trust fully.
Costa has, until now, played without pressure and that does not bring out the best in a man who thrives on being challenged, as well as loved, which is why last weekend Mourinho finally resorted to the only other tactic he had left: dropping him.
Now he is waiting for the response and will hope to see that if Costa, as expected, plays against Bournemouth today.
The problem for Costa is that, for a player who thrives on physicality, he does not look physically able right now. He does not appear fit, and his frustration is boiling over.
He is under scrutiny to get himself back into shape and in form and to end the rumours that he has failed to settle at Stamford Bridge.
The story persists that, like his friend Filipe Luis, who joined Chelsea from Atlético at the same time, he yearns to move back to the Madrid club where he has cult hero status and felt at home.
Filipe lasted just one season at Chelsea; for Costa, it might just be two.
The thing with Costa is that there are recurring themes, similar narratives that exist throughout his career.
He has suffered injuries and setbacks, sustained loss of form, and clashes on the pitch and disputes off it with authority.
Yet, several former coaches have complained that he is misunderstood and harshly treated; that he is singled out because he is Diego Costa (named Diego because his father was a big fan of Diego Maradona).
One reason why his family was so keen for him to play football was so Costa could lead a more disciplined life.
Jaba, the scout of his first team in Sao Paulo, recounts the story of being with a local pastor who said of Costa "If he doesn't play, he'll become a devil" as they watched him kicking a little ball made of paper on the patio inside the church.
Stories are legion about Costa's "crazy" antics, about his pranks and stunts, taking team-mates' cars and trashing their rooms, his late-night barbecues and impromptu kickabouts, his DJing in the dressing-room, the poker clubs, the socialising. And the noise.
Costa makes lots of noise for someone described as shy when he was younger.
From club to club the stories have been the same - as is the warmth towards him.
Team-mates and managers are unanimous about Costa: nasty, aggressive, ultra-competitive on the pitch where he talks of taking it to the limit and going to war.
Off it? The opposite except for one shared trait - an incredible wilfulness.
Even Costa's issue with weight and diet - which he raised himself earlier this season in an apparently selfless defence of his under-fire manager - was a rerun of what has happened in the past.
Diet was first discussed by Javier Hernández, a scout for Atlético Madrid, when he first saw him.
There is a passage in the book 'Diego Costa: The Art of War which recounts Costa's return to pre-season training four days late, having lost his mobile phone and overweight.
"Blame my mum, she's far too good a cook," was Costa's initial flippant reply before he apologised and worked prodigiously hard to shed the extra pounds.
Midfielder Juan Valera, who worked with Costa at Atlético, sums him up: "When he was in good shape he trained like a beast.
"The thing that he tended to neglect was 'invisible training' - following a healthy diet, getting lots of rest and developing an understanding of his own body. He was a bit scatterbrained. He's a one-off."
The Atlético coach at the time was Quique Sánchez Flores, now at Watford, who is effusive in his praise of Costa as a player and a person, breaking into a broad smile, while acknowledging he was someone who enjoyed life, who liked to have a good time, who needed a guiding hand.
To understand fully Diego Costa, though, one has to delve back into his childhood, specifically where he is from: Lagarto in north-east Brazil, a remote, little talked about outpost in the vast country's most impoverished region.
"Beyond the sunset," Mourinho calls it and one theory is that Costa is the way he is because he did not play organised football from a young age and had little experience of being part of a team.
"He's needed all those bookings, the red cards, the fury, the dives, the spitting - you need to make mistakes, you need to learn," said former Atletico sporting director Jesús García Pitarch, arguing that other players go through that phase earlier in their career and away from the spotlight.
Paulo Moura, the president of Barcelona EC, the small club Costa joined when he moved to Sao Paulo aged 15 to work for his uncle, said: "His career was meteoric. He started with us at 15, turned professional at 16. . . he's hard to forget because he's unique. He was a fun boy, a joker. Everyone liked him."
Moura also talks of how "smart" Costa was and how much more physically developed he was than other boys.
Barcelona EC director of sports Robson Vasconcelos, recalled "an explosive temperament. I thought about giving up on him because no club wants a player like that".
Costa was bigger, more able to use his strength, and that has obviously informed the way he has played football from the time when he joined in on a patch of ground at the Boula de Ouro school near his grandparents' home, a social project which he now helps fund and which provides underprivileged kids with free training.
Costa was back in Lagarto last summer, welcoming the local U-15 team to his home, and has spoken about wanting to return there when his career ends, possibly after a spell at the Brazilian club he supports, Palmeiras.
That can wait. For now Costa needs to find his focus. And he needs to find his form. (© Daily Telegraph, London)