The Navy ship near the end of the movie is given the name "U.S.S. Flynn," named after Vince Flynn, creator of the Mitch Rapp character.
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.
The lead role was offered to Chris Hemsworth, but he passed on the role due to scheduling issues. Then, it was rumored that the producers invited Gustavo Goulart to perform the lead role (Mitch Rapp), but this rumor was never confirmed.
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, with the three most recent entries being number one New York Times best-sellers. The series has sold nearly 20 million copies as of October 2015.