Dr. Robotnik (AKA Eggman in the recent games) has been going after Sonic the Hedgehog since the beginning of time. Much like Mega Man and Dr. Wily, Sonic and Robotnik are constantly battling it out over the world. Robotnik's resume includes convincing Knuckles to let him control Angel Island, releasing the god Chaos and flooding Station Square, and activating a death trap for the citizens of earth, set up by his grandfather.

However, Robotnik and Sonic do not just see each other as enemies; they are rivals. No matter what Ivo Robotnik builds, Sonic always destroys it and saves the day. It's become somewhat of a sport to them, a battle of wits. Even when he's on the verge of death, Sonic keeps his cool and rescues his friends, and rather enjoys eluding Robotnik's tricks. As much as they fight, they enjoy the competition, and strive to fight harder as time goes on.

Dr. Robotnik is the mad genius who is trying to take over the world. With an I.Q. of 300, he captures animals to turn them into machines and let them do his bidding. It's up to Sonic and his friends to free these animals and defeat Dr. Robotnik, which has happened time and time again. In more recent adventures, however, Robotnik (who is now known as Eggman, his name in the Japanese versions since the first Sonic game) has been placed in many roles besides a second-hand villain who ends up as being the same boss for each level and getting his schemes foiled.

After two attempts at making the Death Egg (yes, you're thinking Death Star, aren't you?), Robotnik used Chaos, an ancient god, to wreak havoc on the world, and was later turned against by him. He formed the Eggman Empire in Sonic Adventure 2, along with Shadow the Hedgehog and Rouge the Bat, and used the Space Colony ARK's weapon, the Eclipse Cannon, in an attempt to take over the world. After a failure of plans, which nearly destroyed the whole world, and ARK, Robotnik had no choice but to team with Sonic and friends to save the world he was conquering. And then, in Sonic Heroes, he was supposedly behind a scheme to do what he does worst (an attempt to dominate the world, as you may guess), which he didn't even do in the first place; it was all Metal Sonic's doing, who copied Robotnik's data, transformed into him, and imprisoned Robotnik, who was later found by Team Chaotix. And lastly, his role is very small in Shadow the Hedgehog, aside from trying to manipulate Shadow to do his bidding, as Shadow confronted Robotnik to tell him his past.

Overall, Dr. Robotnik has been through a lot. Capture enemies, get pwned by Sonic. Create the Death Egg, get pwned by Sonic & Tails. Rebuild the Death Egg, get pwned by Sonic, Tails, and Knuckles. Summon Chaos, get pwned by Chaos. Etc. You get the point. His accomplishments range as high as being a fully-playable character in Sonic Adventure 2 Battle, but not even all seven Chaos Emeralds can save him from getting trounced by Sonic again and again, or even if his plans backfire on him threatening the fate of the world, and he's forced to assist Sonic. For a man with the I.Q. of 300, he lacks the common sense to match his intelligence in machinery. And just how much spare time and parts does he have on his hands anyway? Gerald, his grandfather, would be proud.

"Farewell Sonic, my admirable adversary." - Robotnik, shortly after launching Sonic into space and watching his capsule explode