Hollywood has tried to bring Vince Flynn's Mitch Rapp series to the big screen for nearly a decade, with actors like Gerard Butler, Colin Farrell and Chris Hemsworth attached at various points. But with the publication of the 2010 prequel American Assassin, producers looked for a younger actor to take on the iconic tough-guy role.
Dylan O'Brien, star of MTV's Teen Wolf, landed the part in 2016 while he was recovering from an on-set injury while filming the final film in the Maze Runner series. Like his character in the film, O'Brien trained to go from a somewhat scrawny kid into a ripped, highly skilled badass.
Rapp's character becomes a vigilante after his girlfriend is killed by terrorists. His action gets noticed by a CIA deputy director (Sanaa Lathan), who has him train under one of their longtime operatives (Michael Keaton), who's still haunted by the student who turned into a terrorist himself (Taylor Kitsch).
Check out the video below to see O'Brien's transformation.
American Assassin hits theaters September 15.