E-105 Zeta (Ｅ－１０５ "ゼータ"?), or E105ζ, is an E-Series robot constructed to serve on board the Egg Carrier. Initially he is a re-colored clone of E-102 Gamma, but later goes through severe alteration and reconstruction to a considerably larger stationary defense unit, built into the core of the Egg Carrier.
Despite being much more advanced, the stationary Zeta is destroyed by Gamma in the Hot Shelter on board the Egg Carrier, releasing the trapped animal inside after Zeta's head exploded.
In Sonic X, E-101 Beta replaced much of Zeta's role, so much that in fact, Zeta only appears on the show in episode 31, "Revenge of the Robot". This is when Gamma comes to the Hot Shelter to, in the game destroy him, he however just inserts a deactivation code through a cable cord in the show.
E-105 Zeta was banished from the Egg Carrier crew, along with Delta and Epsilon, by Dr. Eggman for retrieving the wrong frog when he was searching for Froggy. However, like 'brother' E-101 Beta, Zeta stays aboard the Egg Carrier and undergoes extreme surgery and reconstruction. He emerges as a much larger advanced defense unit, no longer mobile but with seven rocket turrets around his perimeter. E-102 Gamma still manages to destroy him however and releases the bird inside.
- Zeta is one of two E-series robots in Sonic Adventure to receive a physical upgrade and change in appearance (the other being Beta). The remaining E-Series robots, including Gamma, only received enhanced Arm Cannons.
- By altering the texture files of the game, it is theoretically possible to play as Zeta in his regular form instead of Gamma. This applies to all E-100 Series robots.