Riz Ahmed has actively throughout his career sought color-blind casting in his roles so one of the attractive features about this film for him is that the characters' ethnicity doesn't matter with regards to the story.
When Riz Ahmed learned that Michael Pearce was interested in making the film, he immediately pitched himself to the director. Pearce was taken aback by this, not expecting an actor of Ahmed's standing to come calling on him.
The lead character was originally called Marcus in the screenplay. When Riz Ahmed came on board, this was changed to Malik.
To prepare for his role, Riz Ahmed underwent firearm training and spoke extensively with former Marines.