He’d shed some of the weight that had been an issue for his whole career, and against Osasuna on April 3, 2011, a Sunday, Atletico Madrid suddenly had a forward who looked born again.

Sergio Aguero was injured, and Diego Forlan had been dropped after only scoring twice in his previous 16 appearances. Diego Costa was about to outdo that in one evening.

A clinical hat-trick won Atletico the game by three goals to two, with Costa stamping his authority all over the match and indeed the Osasuna players, with goalkeeper Ricardo and defender Lolo both feeling the force of the forward’s desire to succeed. Studs and elbows flew everywhere, but to Costa, it was all part of the game.

That evening, the 22-year-old Costa would have returned to Madrid thinking he’d made it and that his surprise inclusion in the team and subsequent hat-trick had finally sealed his place in Quique Sanchez Flores' plans.

But as with everything in Costa’s career, it wasn’t going to come easily.

As a Brazilian child named after the great Argentinean idol Diego Maradona, as Costa told Jason Burt of the Telegraph, perhaps it was always written that he’d take a slightly unusual route to the top.

He came to football fairly late, with his aggression on show straight away in youth matches in Sao Paulo. But his talent was clear, and it was spotted by agent Jorge Mendes. Soon enough, he was on his way to Europe.

Braga was the destination, and via a loan at Portuguese second-division side Penafiel, he began to get up to speed with European football. It was there Atletico registered their interest in him, buying him for around €1.5 million and loaning him back.

He scored just once for the Braga first team—the winner in a UEFA Cup tie at Parma—before he moved to Atletico.

By the summer of 2007, still aged just 18 and only three years after he'd tried to forge a football career, Costa was in the Spanish capital.

But whereas for some players—such as his new team-mate Aguero—that would be the start of an unstoppable ascent, Costa still had plenty to work on.

His physical deficiencies and the fact he gained weight easily often held him back. Coupled with a suspect temperament, it meant Atletico wanted to see how he’d develop elsewhere.

Despite the sale of Fernando Torres to Liverpool in the summer of 2007, Atletico were happy to send Costa on loan to Celta Vigo in the Segunda Division, where red cards were almost as common as goals, before a similar spell at Albacete the following season.

He was still scoring, but none of these moves seemed to iron out the disciplinary flaws that were so obvious in his game. By 2009, Atletico were happy to sell him to Real Valladolid in order to give him a bit more stability, although they insisted a low buyback clause was inserted in the deal.

Like all the best bad boys, secretly they knew they couldn’t resist him.

And sure enough, back he came in the summer of 2010, finally given a run in the first team and scoring four goals in five games between September and October that year. But he wouldn’t score again until that hat-trick at Osasuna, before which he was dogged by claims he wasn’t good enough to be anything more than backup to Aguero and Forlan.

A serious knee injury before the 2011/12 season muddied the waters further, and with Radamel Falcao now at the club, it was decided yet another loan move was needed if Costa was going to get anywhere near where Atletico wanted him to be.

This one, to Rayo Vallecano, would prove to be the big break he needed.

He scored 10 times in 16 games, eventually returning to Atletico fitter, hungrier and with a clearer mindset. He wouldn’t look back.

It was now 2012, and Costa was crucially given the backing of new Atletico Madrid manager Diego Simeone, who perhaps saw something of himself in the fiery South American.

There were numerous spats and disputes, but Simeone stuck by Costa through thick and thin, playing him as a foil for the prolific Falcao. He managed 20 goals in all competitions—including eight during Atletico's triumphant run to the Copa del Rey. For once in his career, Costa appeared to be smiling.

That 2012/13 campaign was, in many ways, his breakthrough at the top level, and his success prompted Liverpool to bid £21 million—matching the forward’s release clause, per Ben Smith of BBC Sport—to try to bring him to Anfield to partner Luis Suarez, a frightening prospect for any defence.

But Costa turned down the Reds and the riches on offer in the Premier League. He felt he had unfinished business with Atletico.

And with Falcao departing for AS Monaco that summer, he was now the main man.

Simeone had made the intelligent move of bringing in David Villa from Barcelona, and the experienced Spanish forward dovetailed perfectly with Costa, often making intelligent runs and trying to take the heat off his hot-headed team-mate.

Because Costa was a marked man in La Liga now.

He scored twice in Atletico’s first league game of the season, against Sevilla, before his winner in the Madrid derby at the Santiago Bernabeu in late September signified this Atletico side was a genuine title challenger. Then a stunning goal against Getafe in November was nominated for the Puskas Award.

He'd managed a remarkable 23 goals in 20 games by the midway point of the 2013/14 season, with his strikes securing a place at the front and centre of the Primera Division title race, as well as progress in the Champions League, in which he scored three times across the two legs against AC Milan in the first knockout round.

Clearly feeling at home in Madrid, it was during this campaign Costa decided to switch his international allegiance to Spain. And given that that would take some time to resolve, he was free to focus solely on being Simeone’s attack dog in their hunt for glory.

It worked.

Goal after goal propelled Atletico closer and closer to a historic title, with Costa’s solitary second-half strikes in the March victories over Espanyol and Granada proving crucial.

Again, controversy wasn’t far away, with Sevilla midfielder Geoffrey Kondogbia accusing Costa of racism after a Copa del Rey tie, per AS. But on the pitch, he had become an Atletico icon. Then disaster struck.

After helping his side to the Champions League final, an injury on the final day of the league season at Barcelona—where Atletico won the point that secured a first title in 18 years—left him struggling to make the Lisbon showpiece against Real Madrid.

In the event, he played, but he only lasted nine minutes. His side eventually lost out to their city rivals in heartbreaking fashion.

Costa never played for Atletico again, joining Chelsea that summer for a fee of around £32 million, packing his bags and taking his special brand of antagonistic football to London—where he won the Premier League in his first season.

He’s not been forgotten in Madrid, though, where his fight to prove himself at Atletico and in Spain proved compelling.