From Halopedia, the Halo wiki
Alex Garland (born 1970 in London, United Kingdom) is a British novelist and screenwriter.
He was designated to be a screenplay writer with D.B. Weiss in 2004 just before the Halo 2 launch. It was around that time that Peter Schlessel, a Hollywood writer, had started to meet with Bungie staff to discuss plans for a potential Halo movie.
Garland, whom Bungie selected for writing the screenplay, is on the list of Schlessel's approved writers. Later, Microsoft released Garland's completed screenplay to various Hollywood studios on June 7, 2005, looking to be paid a $10 million fee as well as the studio's agreement to adhere to guidelines set by the game's developers.
He is also the producer of 28 Weeks Later.