E-123 Omega is the last of Doctor Eggman's E-100 series robots, specifically designed to contain and control Shadow the Hedgehog. In his first appearance in Sonic Heroes, Eggman seals Omega within an abandoned base, along with Shadow, until Rouge the Bat accidentally releases Shadow from his stasis pod. Infuriated at being sealed, Omega decides to team up with the two to obtain revenge on Eggman and prove that he is Eggman's most powerful creation. He returns with the same goal in Shadow the Hedgehog, and teams up with Shadow in certain levels to destroy Eggman's robots. During Sonic the Hedgehog, he is playable after Rouge orders him to support Shadow many years in the future. He is playable in Sonic Chronicles: The Dark Brotherhood.
Omega has an array of weapons concealed in his arms, including machine guns, flamethrowers, missile launchers, and energy cannons. He can also retract his hands in order to attach a spinning Shadow and Rouge in their place, either using the two as melee weapons or firing them. Omega can use jet boosters built into his back to help accelerate and hover. He also has a range of sensors in order to detect and locate enemies. Omega is voiced by Taiten Kusunoki in all Japanese media, and Maddie Blaustein (previously Jon St. John and Andrew Rannells) in English media.