E-123 Omega (Ｅ－１２３ "オメガ", E-123 Omega?) is a fictional robot from the Sonic the Hedgehog series. He is considered a spiritual successor to E-102 Gamma who is part of the same robotics production line in the series. He was created by Dr. Eggman as the last and most powerful E-Series robot,[8] and is out to eliminate him due to harsh mistreatment and lust for revenge. Omega has helped Shadow (and to a lesser extent, Rouge) in several games and while not being a major character, is popular enough in his own right and has established himself as a main character.

While Omega, as a robot, is largely emotionless, he is capable of understanding those of others, and reacting appropriately. For example in Sonic Heroes, when Team Dark is lead to believe that Shadow may be an android created by Eggman, Omega comforts a depressed Rouge (albeit in a distant, matter-of-fact matter) by saying that they needed the original to make a copy, thus meaning that the real Shadow is still alive. In Sonic the Hedgehog (2006), he shows depression and anger when Mephiles reveals that Omega is the one who will trap Shadow in the future after the world blamed Shadow for the release of Iblis. It is also possible Omega is superstitious, as he believes in omens such as the appearance of stormy weather, though this might have been because of his scanners picking up a powerful magnetic field.[17]

Like E-102 Gamma, Omega has a free will and a personality. However, he is considerably less noble than Gamma; while Gamma destroys only what needs to be destroyed, Omega destroys anything that could possibly pose any kind of threat to himself or his mission.[18] From his quotes, he thinks other Eggman robots are inferior to him,[19]dismissing them as "worthless consumer models", especially the E-2000 model.[20] He hates side tracking especially when it comes to locating Eggman.[21][22]Omega is also very proud and feels embarrassed after he is defeated by less powerful Eggman robots.[23]

It also seems that he lacks any sort of negativity towards Sonic and his friends, and didn't even recognize them during their first meeting in Sonic Heroes, as can be heard when the player finishes the Team Battle using Omega.[24] This is probably because Omega was made to contain Shadow the Hedgehog and not as a means to defeat Sonic. However, he does not appear to hold them in high regard, referring to them as 'meatbags' in Sonic Chronicles: The Dark Brotherhood.

Omega's only goals in life are to take revenge on Eggman for disabling him and destroy the doctor's other robots to prove himself superior. These two goals are absolute above all else in Omega's eyes. As a result, he tends to be extremely headstrong and reckless, unlike his teammates on Team Dark who have more common sense. In Sonic Forces, he performs what is supposed to be a recon mission on Eggman's base, and, rather than sneaking in to get information, storms in guns blazing in an effort to purge the base of every robot within, despite his orders having nothing to do with extermination.[25] At one point in Shadow the Hedgehog, Omega made a comment about how he would "reign supreme".[26] Some fans have taken these words quite literally, and believe that Omega wants to take over the Eggman Empire and become a robot overlord in the style of Metal Sonic. However, subsequent games have shown this less believable, and it is generally taken to mean that he wishes to prove himself as the greatest of Eggman's robots.

Omega is fairly loyal and dependable when you're on his good side, a bit of a holdover from his original purpose as a servant, and he's not incapable of looking past differences to forge alliances. He also genuinely cares for Shadow and Rouge and sees them as friends, and trust their word over everyone else's; for example, in Sonic Chronicles: The Dark Brotherhood, when the party discovers him, he tries to attack Eggman the moment he sees him, and Tails' attempt to explain that Eggman is on their side only makes Omega believe that Tails has gone insane and decides to attack him as well, only believing that Eggman is working with them and standing down when Shadow and Rouge confirm this.[23] In addition, he will temporarily abandon his vengeful quest against Eggman (or even indirectly work with him) if he detects a bigger threat, as evidenced by his participation in the battle against Metal Madness, Solaris, or the Nocturnus Clan.

Stereotypical of most robots, Omega tends to use somewhat lengthy words instead of usual human speech. An example of this is when he uses "negative"[27] or "affirmative"[28] instead of simply saying yes or no. Although he has been known to use typical human speech before,[29][30] such as one of his Hint Ring lines from Sonic Heroes: "Looks like those guys are guarding that case."

Notably, in all of his appearances (barring the 2006 Sonic the Hedgehoggame, in which he behaved in a manner stereotypical of old robots), he makes odd, often erratic movements, such as spinning his head as if it's on a 360 degree axis in many circles and rotate his entire upper body the same way during confrontations with Eggman in Shadow the Hedgehog. Whether this is a programming flaw or intentional is not revealed. Also in Sonic the Hedgehog, when Omega is standing still, he makes odd movements as if he's doing warm up exercises.