E-105 Zeta was very different from other units in the E-100 Series. Possessing a primarily purple color scheme, Zeta's upper torso and head resembled those of the typical E-100 units, complete with a round-shaped upper body with a white stribe down the middle, and a platform-like black head with a yellow shade and green cylindrical eyes. However, from its upper torso and down, Zeta resembled mostly a large stationary tower. It was round on the sides, with its upper torso section being raised above a wide plaform-like section with a black bottom, and had green lights in various places. Most of Zeta rested upon a gray high-tech pillar. It also had several pipes attached to the platform below its upper torso, all of which were bend downward.
E-105 Zeta, along with Beta, Gamma, Delta and Epsilon, were created by Dr. Eggman as a part of the Doctor's new E-100 Series of robots. Zeta himself ended up being designed as a stationary machine unit of unknown function in the Egg Carrier's engine room.
After the Egg Carrier crashed, Zeta was discovered by Gamma, who had set out on its own to "save" its robotic brethren. Zeta was soon after reprogrammed by Gamma, who deleting its master entry of Dr. Eggman. This caused Zeta to shut down.
E-105 Zeta did not demonstrate much of a personality during its time, appearing as no more than a lifeless stationary machine.
- Zeta's role was largely replaced by Beta in Sonic X. Unlike in Sonic Adventure, Zeta does not participate in the hunt for Froggy and the circumstances of its reconstruction are unknown. In the games, Eggman rebuilt it after it got the wrong frog, while in Sonic X, Zeta appeared for the first time in its rebuilt version.