When Nightwatch first came to the station in 2259 Zack ecstatically joined, based on the 50 credits he would be paid in addition to his regular paycheck a week. Slowly he became aware of the fascist nature of Nightwatch, and after witnessing firsthand the tactics they performed on the station to a shopkeeper who badmouthed Clark's administration, he agreed to help remove the organization from the station.
Years later, he ethier resigned or retired from Earthfore and went back to Earth for a while, but got bored there. In July 2280 he returned to Babylon 5 and was head of security, six months before station's decommissioning in January 2281.
Zack was a good friend of Michael Garibaldi. When Garibaldi disappeared in December 30, 2260, he searched for him. On January 17, 2261 he successfully rescued him and brought him back to Babylon 5.
Zack had been fired from several jobs and had many personal problems that proved to be a problem in keeping a job for very long. When he sobered up he got a job working for his old friend. As Garibaldi said to Zack during a discussion: "You had a lot of problems before you came here, and I know, I know you had some problems after you got here, too. But did I say anything to you about it? No. You wanna know why? Because I knew, I knew you would work it out, and you always did." 
He also was a friend of Lyta Alexander. She discovered that his feelings were more than simple friendship when he tried to deter her from staying with the rogue telepaths around Byron,  but she never returned his affection.
|Main Characters (Babylon 5)|
|Commander Jeffrey Sinclair Captain/President John Sheridan Lt. Commander/Commander Susan Ivanova Security Chief Michael Garibaldi Ambassador Delenn Dr. Stephen Franklin Talia Winters Lennier Marcus Cole Captain Elizabeth Lochley Vir Cotto Lieutenant Warren Keffer Na'Toth Security Chief Zack Allan Lyta Alexander Ambassador/Citizen G'Kar Ambassador Londo Mollari|