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‘American Assassin’ actor Dylan O’Brien discusses the intense training involved in preparing for the movie.
USA TODAY

LOS ANGELES — Dylan O’Brien knew there would be online turbulence when he was cast as black ops killer Mitch Rapp in American Assassin.

O’Brien, 26, understands that fans of Vince Flynn’s best-selling novels might not visualize the star of MTV’s Teen Wolf as the guy to take on the lethal hitman, a part that Thor’s Chris Hemsworth turned down for scheduling reasons.

“Maybe people didn’t assume I could step into this role and be believable,” says O’Brien. “All’s fair in filmmaking, but no one knows you like yourself.”

He knew he could defy those expectations, unleashing an angry young killer-in-training in the edgy origin story American Assassin (in theaters Friday), a portrayal fueled by O’Brien’s emotional return from an injury last year on the set of Maze Runner: The Death Cure that nearly ended his career

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He was cast in Assassin while holed up in his L.A. home, feeling angry and depressed as he recovered from a serious head injury suffered when he was thrown from the harness of a moving vehicle during a stunt. 

“There’s the physical recovery. And you’re going through a post-traumatic psychological recovery as well,” O’Brien says. “Your mind is so consumed with doubt, you’re just beaten down. And you feel guilt in a really weird way.”

Not only was Maze Runner filming postponed because of the accident (the movie will be out in January), but he had doubts whether he could take on any parts, much less an action role.

“You start experiencing things that are abnormal, you’re just not yourself. What you don’t realize is that you’re reacting to a situation where your brain experienced severe trauma,” says O’Brien. “You’re irritable and isolated and you’re angry. So angry. Because that can give…