E-123 Omega

Omega was built and designed as the one hundred and twenty third and final model of Eggman's E-100 Series robots, specifically made for combat against Eggman's greatest enemy, Sonic the Hedgehog. He wasn't activated until a year later and had been left in storage for all that time.

After reactivating the war machine in the Eggdome in the ruins of New Megaopolis, Eggman gave Omega his first mission to hunt down and destroy E-102 Gamma. At first, Omega refused as Eggman had left him in storage for over a year and he was built to destroy Sonic the Hedgehog, but his mission was to destroy something else. Eggman informed Omega that he alone would kill Sonic and threatened to put him back in storage for a decade if Omega did not follow orders. Omega then left to begin his mission as Eggman and Snively watched him leave from the landing bay of the Eggdome.

After locating E-102 Gamma in the remote mountains hours later, Omega was forced to battle the rogue robot as well as G.U.N. agent Shadow the Hedgehog. Delighted to fight an opponent stronger than Sonic, Omega focused on Shadow until Gamma fired at him and Omega realized that his mission objective was there too. Shadow then attacked Omega and told Gamma to get to the extraction point while he distracted Omega. Intent on completing his mission, Omega temporarily disposed of Shadow by using his arm cannon to capture and blast him away.

Omega then chased after Gamma and exchanged monologues via radio. While Omega stated how he was superior to Gamma in every way, Gamma pointed out that Omega's superiority had downsides that could be used to his advantage, and that his own downsides that Omega pointed out were advantages for him as well. Eventually, Gamma admitted he was outdated, just as Omega said and that the resistance forces would need something more than him to fight the Eggman Empire. Accepting this as surrender, Omega prepared to give Gamma a "glorious destruction" by unleashing all his weapons on him at once out of respect. Telling Omega his soul will remain even if he is destroyed, Gamma uploaded some of his programming into Omega before his robotic body was destroyed by Omega's barrage. A brown Flicky then flew away from what remained of Gamma afterwards, while Omega became overwhelmed by his new programming and free will.

After Shadow arrived seconds after E-102's destruction, "Gamma" spoke through Omega, informing them that he uploaded his coding into Omega. The coding integrated into Omega and the two entities became one. With a new feeling of purpose, Omega was convinced by Shadow to join G.U.N. and fight against the Eggman Empire like Gamma would have, and to also get his revenge on Eggman for keeping him in storage and wasting his potential. After Omega created a grave marker made out of rocks for Gamma, he and Shadow were picked up by a G.U.N. helicopter and brought back to G.U.N. HQ where Omega met Chief Commander Abraham Tower, who considered Omega as an excellent "replacement" for Gamma. Then Omega was examined by Hope Kintobor, who was amazed to find out that half of Omega's body weight was in ammunition, jokingly calling him a "monster" when she discussed the examination with Shadow and Rouge in the recreation room later on.