E-105 Zeta (Ｅ－１０５ "ゼータ",E-105 Zeta?), 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 in the engine room of the Egg Carrier.
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 his "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 Flicky inside.
To defeat E-105 Zeta, to the player must destroy the large turrets surrounding the robot. They should run around the arena and flash Gamma's targeting laser toward the robot when possible. When E-105 launches a volley of missiles, the player must keep moving to lure them off course, or target and destroy them. Each time Gamma blows off a turret, E-105's energy level drops. When the turrets are all destroyed, E-105 will be defeated.
In the anime series Sonic X, E-101 Beta replaced much of Zeta's role, with Zeta only appearing in "Revenge of the Robot". This is when Gamma comes to the Hot Shelter to destroy him. However, he just inserts a deactivation code through a cable cord in the show.
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.
Zeta is the only member of the original E-100 series from Sonic Adventure to feature a different design than E-101 Beta (except for ZERO).