First appeared in A Spider in the Web, as one of Garibaldi's security team members.  He joined up with Nightwatch for the extra fifty credits a week (In the Shadow of Z'ha'dum), but was not entirely supportive of their purpose (The Fall of Night, Voices of Authority) until he eventually helped Sheridan and Garibaldi dispose of them in the breakaway from Earth (Point of No Return).

He eventually replaced Garibaldi as Chief of Security after his resignation (Epiphanies), and he never seems to find uniforms that fit (Voices of Authority, Atonement).  His first obligation in his new post seemed to entail trying it on with Lyta Alexander (Epiphanies, Moments of Transition, Thirdspace) - unsuccessfully (Strange Relations).

He remains on Babylon 5 for nearly 20 years, returning briefly for the decommissioning ceremony (Sleeping in Light).

Played by Jeff Conaway, who appeared as one of John Travolta's gang members in Grease (and was even briefly married to Olivia Newton-John's sister).

Zack Allen