A sniper in Lyons' Pride, Colvin is 40, friendly, and warm to everyone; he has priest-like tendencies. To him, combat is like worship, and he treats his rifle as a holy object and his targets as the unfortunate victims of his God's wrath. He says a prayer for the soul of each mutant he kills. He's extremely experienced, and completely unflappable: all according to God's will.
Colvin is a member of the Lyons' Pride, which he considers his family.
Knight Captain Colvin is likely a reference to the character Private Daniel Jackson (played by Barry Pepper) in the movie Saving Private Ryan. Like Colvin, Jackson is an army marksman who says a prayer before taking each shot. Interestingly, Colvin's fellow Lyons' Pride member, Knight Captain Dusk, also references Jackson with her quote "Put any mutie bastard within one mile of me and my rifle and, well... pack it up troops. Fight's over."