E-123 Omega is the last in the E-series of robots created by Dr. Eggman. He has a deep hatred for Eggman, who locked Omega up in a cold, dark room for years, and now wants to destroy all of Eggman's other robots so he can be the best. He's a member of Team Dark with Shadow and Rouge.
Omega was voiced by Jon St. John in his debut appearance, Sonic Heroes. When the cast was replaced, Maddie Blaustein became Omega's voice from 2005 until her death. However, during development, the lines she recorded for Shadow the Hedgehog were replaced by Greg Weber. It was necessary to redo Omega's lines, but since she was unavailable, Jeff Kramer at Webtone Productions in San Francisco, California. Her voice was, however, heard in the finished product of Sonic 2006. When SEGA began using a Los Angeles-based voice cast starting with Sonic Colors, Vic Mignogna took over as Omega.