Name: Robot Zeta
Super? (Has Super Powers/Special Abilities/Technology): Yes
Number of Appearances: 1
Ally: Robot Delta
Ally: Robot Epsilon
Gender: not applicable
Note: an Ultra-Robot; fought with, destroyed by Captain America
Robots Delta, Epsilon and Zeta were three Ultra-Robots that Lucifer had left stashed in a secret desert location in the American Southwest during a previous attempt to invade Earth (X-Men vol. 1 #21). When Lucifer returned to Earth again, he battled the Falcon in Harlem, New York, but he felt he wasn't strong enough to defeat the hero. So he returned to the Southwest, retrieved the three Ultra-Robots he had left there, and brought them to New York to terrorize Harlem and vanquish the Falcon.
Ultimately Steve Rogers (retired temporarily from being Captain America, but still heroic and quite capable) entered the fray and defeated the Ultra-Robots. Rogers tricked them into running into each other and destroying each other.
The names (or specific unit designations) of Robots Epsilon and Zeta can be seen in panel 5 on page 16. Robot Delta is attacking Steve Rogers and tells his two fellow Ultra-Robots: "Robots Epsilon and Zeta-- block his path at all costs!"