Colin Mallory is Quinn's brother whose existence Quinn discovered at the beginning of the fourth season and finally tracked down in the episode "Oh Brother, Where Art Thou?". Raised on an Amish-style world he was not accustomed to modern technology but like his brother was fascinated enough to invent things even on the low-technology world where he was raised.
Colin was involved in the same incident that saw his brother Quinn removed from the series; during the slide from one world to another, Colin and Quinn were targeted by an evil scientist and Colin succumbed to the same fate as the scientist - 'unstuck' - travelling between dimensions without any control as to when and where he travels.
Played by Charlie O'Connell, Jerry O'Connell's real brother. Charlie had also previously acted in Sliders as Kit Richards (As Time Goes By) and Officer O'Hara (Dragonslide).