Dr. Eggman

Dr. Ivo Robotnik (ドクター・ロボトニック Dokutā Robotonikku?, lit. "Doctor Robotnik"),[4] better known by the alias Dr. Eggman (ドクター・エッグマン Dokutā Egguman?),[5] is the main antagonist of the Sonic the Hedgehog series. He is a human and the arch-nemesis of Sonic the Hedgehog. This large scientist with an IQ of 300[1] dreams of dominating the world, but his constant plots to create his Eggman Empire are always thwarted by Sonic and his friends.

While the doctor's plans initially consisted of building incredible armies by turning animals into robots and using them to dominate the land, Dr. Eggman's schemes have since branched into much more global threats as he built war machines, used nuclear devices to threaten entire nations, and even relied on mythological and ancient deities bent on destruction to achieve his goals. Eventually, the mad scientist has gone as far as to target the entire universe and cooked up schemes to control time and space itself.

While all these plans end in failure thanks to the continued efforts of Sonic and his friends, the mad doctor is somehow always able to slip away from certain death or imprisonment and escape at the last moment, making him a constant threat to the universe and a thorn in Sonic's side.

A Super Mario World
Doctor Eggman is one of the minor antagonists in A Super Mario World. He is briefly seen in the second episode riding his Egg Mobile, and he reveals that he aided Bowser to build their "Bowser-Eggman Cruiser" (a flying Bowser Castle-esque mechanized unit) after Mario, Link and Cloud Strife confront Bowser on said castle's roof. Eggman abandons Bowser after he realizes his work is done and is no longer seen throughout the remainder of the series. Because of this, he is the only antagonist of the series that did not get killed by the heroes.

Oddly, Eggman technically worked alongside his arch-enemy Sonic the Hedgehog and Knuckles the Echidna, who acted as Bowser's guardians. It is unknown whether any of these characters were aware of this.

Video Games
Dr. Eggman is unique among other World Bosses in that he also acts as the boss of the regular levels. At the end of each level in Mobius, Dr. Eggman attacks the player with one of his various machines using over the years, echoing his role in the 2-D Sonic games.

While he seemed to be allied with the Forces of Legion, he was actually working for the Villain Alliance, working with Dr. Wily to harness Twisted Reality's dark energy without Legion knowing.