The lead role was offered to Chris Hemsworth, but he passed on the role, due to scheduling issues. Then, it came up that the producers invited Gustavo Goulart to perform the lead role (Mitch Rapp), but this rumor was never confirmed.
Michael Keaton was initially apprehensive about playing Stan Hurley, who is portrayed as a somewhat crazy, former CIA operative. Keaton did not like the idea originally, due to Keaton's well known liberal views. However, after reading Vince Flynn's novel American Assassin, Keaton felt like he could connect with and channel the character of Hurley.
Dylan O'Brien won the part of Mitch Rapp, beating more established older actors. Being in his mid 20s, the hope is that the actor grows as the envisioned movie franchise progresses. Also, since this movie is based on a prequel novel, it provides the opportunity to start at the beginning of Rapp's career.
"American Assassin" is one of fifteen novels by Vince Flynn set in the world of counterterrorism operative Mitch Rapp. Every book has been a New York Times best-seller, the three most recent entries have been number one New York Times best-sellers, and the series has sold nearly twenty million copies as of October 2015.
Veteran stuntman and martial arts world champion Buster Reeves (Instructor) and Michael Keaton (Stan Hurley) share the Batman mantle. Reeves doubled for Christian Bale and performed Batman's stunt fighting in The Dark Knight trilogy, and Keaton played the Caped Crusader in Batman (1989) and Batman Returns (1992).
Actor David Suchet has played both sides of the cinematic espionage genre. In this movie, he plays CIA Director Stansfield whose objective is to stop terrorists from producing & using nuclear weapons. However in Executive Decision (1996), he played the lead terrorist who hijacks a commercial American airline and attempts to detonate highly-explosive nerve gas over the east coat of the United States.
In the books, Mitch Rapp's girlfriend was killed in the Pan Am flight that was blown up by a terrorist over Lockerbie, Scotland on 21 December 1988, a historical event. In the movie she is gunned down on the beach of Ibiza, Spain.