Zack Allan is a character in the fictional universe of the science-fiction television series Babylon 5, played by Jeff Conaway. He regularly appeared in the show from season 2 onwards. During the second and third seasons of the series he was a security officer on the Babylon 5 station. In the fourth season, he was promoted to become Babylon 5's Security Chief and he retains that position through to the end of the series' fifth and final season.