Before Bowser/Mecha SagasEdit
From the beginning, his goal was to turn the animals of Mobius into his robotic slaves and build the city from which he would rule his empire, Eggmanland. To his end, he launched repeated schemes involving acquiring the Chaos Emeralds or tapping into something else usable as a weapon. Despite his best efforts, Sonic and his friends stopped him over and over. Eggman plays an important part in RowdyRuff Boys Z, albeit a small one.
Before his debut in Episode 13, he has, on multiple occasions, attempted world conquest. One of these attempts included controlling Chaos, while another included trying to set free Shadow the Hedgehog. Both of these attempts failed, however.
His last attempt to take over the world, by this timeline, is when he upgraded the real Metal Sonic to take over the world, however; Metal turned on him and tried to rule it himself.
Like most villains, Dr. Eggman is defined by his ego. His idea of a perfect empire involves his image plastered everywhere and even his former fortress, the Death Egg, has his face on it. He generally considers himself a genius without peer, save possibly his grandfather, Gerald Robotnik. When his plans break down, though, he loses his temper rather easily and can have some childish behavior.
Despite his evil ways, Eggman has been shown to fight against a greater evil when his own life or that of Mobius is threatened. His reasoning is mainly that he can't exactly conquer the world if there's no world left to conquer.
Eggman, though somewhat tougher than he looks, is not a very physical fighter. He can move surprisingly fast when fleeing, but doesn't possess notable strength or speed in combat. He can take a few hits, however, and is good at fighting with his technology.
Eggman's greatest skill is when he's in the cockpit of one of his robots. He has been shown to be an ace pilot and highly skilled in controlling his creations, making him much more dangerous.