On Thanksgiving Day in 2011, while the rest of his teammates were taking tryptophan naps, Oklahoma City forward Serge Ibaka arrived at the Thunder's practice facility for a workout. He wasn't supposed to be there – even the security guards were off that day – but, undeterred, Ibaka used his passcode to enter. He was later fined for breaking team rules, but according to head coach Scott Brooks, "Every day is a day of work with him. He does not take days off. He comes back at night. On the court, in the weight room, in the film room."

That discipline has carried Ibaka, 23, all the way from his war-ravaged homeland of the Republic of Congo to the NBA elite. He led the league last season with 241 blocked shots – 106 more than the next guy – while playing just 27.2 minutes a game. He made the All-Defensive First Team and finished second in voting for Defensive Player of the Year. Now in his fourth season, he is the defensive key to the Oklahoma City Thunder's young core, a game-changing force with a bright future to match his $49 million contract extension.

Born in 1989 in Brazzaville, Ibaka grew up in a family compound of small brick homes. In the courtyard, his grandfather ran a low-key social club, playing music and serving drinks. Serge shot hoops in the street with a miniature soccer ball, emulating his parents – his father was a 6-foot-7 forward for the Congolese national team, and his mother played for the neighboring Democratic Republic of Congo. "I liked growing up in a family atmosphere," he told an Oklahoma paper during his first year in the U.S. "We took care of each other."

He lived a modest but comfortable life until his grandfather died, followed by his mother, both of whom had fallen ill.

When Serge was seven, war erupted – a localized conflict that became part of the broader Congo wars that, between 1998 and 2003, killed an estimated 5.4 million people. He fled with his grandmother to a town near the northern border until the violence subsided some three years later. With no home to return to, Serge moved in with his father, whose work as a customs agent frequently took him across the Congo River. But one day, during a period of political tension, his father was arrested while on a work trip in Kinshasa, the capital of the DRC, and jailed for two years.According to Ibaka's Spanish agent, Pere Gallego, who first signed the prodigy to a European team in 2007, he has spoken of a period when he slept on the street and snatched scraps from restaurant tables. When Ibaka is asked for details today, his easygoing manner shifts. "It was a hard time," he says, voice trembling. "I don't like to talk anymore about that time. It's in the past now. I don't want to go back."

It was right after this hard time, however, that Ibaka's formal basketball education began. When he was 14, his grandmother sent him to train with one of his father's old teammates. On a dirt court, using cardboard insoles to cover the holes in his sneakers, Ibaka sharpened his game. Every morning before dawn, he would jog across the city to a steep hill dotted with earthen houses and sprint to the top. Soon, he was competing for the Republic of Congo's under-18 team at the 2006 African championships. Anicet Lavodrama, a scout for the Cleveland Cavaliers and an ex-player who'd competed against Serge's father, was watching. "There was no doubt he belonged in the NBA," Lavodrama says.

Ibaka left for Europe a year later. Lavodrama recommended him to Gallego, who placed him on a team in the Barcelona suburbs. Scouts flocked to the region that season, and Ibaka was picked 24th overall in the 2008 draft. Onstage at Madison Square Garden, 6,000 miles from his birthplace, he flashed a grin that suggested he was right at home.

Today, six years after leaving Brazzaville, Ibaka inhabits a very different world. He has deals with Adidas and Sprite, and a celebrity girlfriend, the singer Keri Hilson. He lives in a three-story townhouse five minutes from Chesapeake Energy Arena, next door to one of his new best friends, Kevin Durant. "He's always coming over, just walking into my house, eating my food," Durant says, laughing. "All my Pop-Tarts and chips." They are like brothers now, only one speaks Lingala better than English.

On a crisp afternoon in November, Ibaka sits beside the Thunder practice court in black jeans and a snug black tee. His deltoids bulge – he's gained 15 pounds of muscle over the past three years. He is the last player here, after shooting threes, lifting weights, and icing his thighs post-practice. "Blocking shots is about preparing your body," he says. "You have to lift weights – and your legs, make them solid. But from there, it's mental. Like, this guy has got two, three baskets. He isn't going to put the next one in."

That attitude drove a monster block of a LeBron James dunk during game two of the 2012 NBA Finals, one Ibaka celebrated with an irreverent finger wag. "Ibaka's one of the few guys in the league that can match LeBron in terms of size and strength," says ESPN analyst Chris Broussard. "He's very athletic, and he's got great timing. Even if he doesn't block the shot, he's changing the shot because you're thinking about where he is."

Ibaka is a work in progress, but teammates expect him to grow from a blocking specialist into a solid scorer. He's already moving in that direction, with more minutes and more points this season than last. "His offensive game is expanding every single year," Durant says. "Just look at him now – he's shooting threes."

During the summer, Ibaka returns to Congo to visit his grandmother, run a basketball camp, and volunteer with UNICEF, helping children who live on the streets as he once did. Asked how it feels to finally make it, he answers without hesitation. "I have not arrived," he says, glancing up through a bay of skylights. "When I was drafted, I thought, I still have a lot to work on, many things to do in order to arrive. Yet even now, I have not arrived. But I will."