Reg Cole (presumably christened Reginald) is an almost entirely tragic figure, a lonely man performing a thankless, necessary task, and viewed by the vast majority as walking wallpaper. Even with a gun in his hand, perhaps especially so, the witnesses' best description is, "Ordinary, really.".
Reg has been working maintenance for the Manchester Gazette for eight years, yet the people who brush past him everyday have not the slightest recollection of him. In frustration that his life amounts to nothing, Reg grabs a gun and hostages at the paper, looking to force Jackie Queen to write at least a memorable obituary for him. He is an over-educated man for the menial function he fulfills, and chafes constantly and silently, building and nursing resentment.
He shoots Gene Hunt in the chest - or rather, the hip flask, which saves his life as well as the DCI's. As Reg's actions occur while Sam Tyler is 'on a deadline', the DI worries that this is going to be his last case in any timeline.
Reg appears only in Series 1: Episode 6 (Life on Mars).