If others rolled their eyes at Mr. Stanfield’s acting dreams, his mother believed in him and called him her superstar. Part of their connection was forged by pain. Mr. Stanfield said he would get involved when his mother and stepfather fought, and scream at him to leave her alone. When she could, she would drive him to Los Angeles for auditions. When she couldn’t, Mr. Stanfield tried to hustle up money for the train. And when there were no lawns to mow or cars to wash, he’d panhandle.

For a good while, nothing much happened in Los Angeles beyond a series of awkward auditions. Eventually, he was connected with Mr. Cretton, who cast him as a teenager living in a group home for his 21-minute master’s thesis project, “Short Term 12.” The film made waves at Sundance in 2009, and back at high school, Mr. Stanfield proudly handed out DVD copies. He told himself that even if he never got another Hollywood job, he’d be satisfied (he says he still keeps that attitude today, and that it’s been a ballast). And for a few years, it looked as if that would be it, because he couldn’t land another part. He worked at the marijuana place, and then briefly moved to Sacramento to live with his dad, where he sold AT&T contracts door to door until he got fired over outstanding marijuana warrants.

Around 2012, Mr. Cretton found the financing to make his short into a feature, and put new actors — among them Brie Larson and Rami Malek — in every role. But no one felt right for Mr. Stanfield’s old part. And Mr. Stanfield was nowhere to be found. He’d fired his manager, and dropped his old email and phone number. Mr. Cretton eventually tracked him down on a messaging board. Mr. Stanfield drove down with his mom from Victorville, riven with certainty. “Never was I more ready,” he said. He read through a few scenes in Mr. Cretton’s living room, and when he looked up, he saw Mr. Cretton was in tears.

The film debuted to raves, and Mr. Stanfield was nominated for an Independent Spirit Award. Yet for months afterward, he drifted about Los Angeles lucklessly, alternately sleeping in his car or on Mr. Cretton’s couch, as all of his auditions led to naught. Lying in his own bed, Mr. Cretton would silently send anguished prayers to the Hollywood gods, imploring them not to mess this one up. “Someone recognize this dude,” Mr. Cretton recalled pleading.

And finally, someone did.

It’s hard to capture in words the place Mr. Stanfield goes to in his performances, where everything gets stripped away except for something so intense and pure it vibrates off the screen. In acting lingo, he is wide open. Mr. Riley, the director, said Mr. Stanfield feels everything his character feels, and also doesn’t give a fig what that might look like. “He’s raw, he’s experiencing something that needs to be felt right then,” he said. Hiro Murai, who has directed the majority of “Atlanta’s” episodes, said Mr. Stanfield was the most intuitive performer he’s worked with yet. “He sort of lets himself free-fall in the moment,” Mr. Murai wrote in an email. “He’s fearless that way.”