Gannon was once an Enclave infantryman operating in the Southwestern United States. At some point, he deserted the Enclave and joined the Followers of the Apocalypse at Hoover Dam.
Arcade was going to appear in Van Buren, the canceled Fallout 3 by Black Isle Studios. While the Denver design document refers to him being in Hoover Dam, the Hoover Dam design document does not mention Gannon, which indicates that he was added into the game after the latter was written. This character, with some re-writing, appears as a recruitable companion and Followers of the Apocalypse member in Fallout: New Vegas.