Dr. Ivo Robotnik (I refuse to call him 'Eggman', fuck you Japan) has long terrorized the planet Mobius. But what would drive a man to put small animals inside of robot versions of different animals and use them to wage war against his fellow man, as well as against animals who are sentient and humanoid such as Sonic, Knuckles, and Princess Sally? This blog has uncovered audio from Robotnik's early days working in his lab, along with his nephew and lab assistant Snively, that might shed some light on things:
Robotnik: Snively! Check it out, I built a big ass robot caterpiller. I call it Cater-killer. Get it?
Snively: Yes Uncle very clever. Uncle Ivo, I don't wanna be a dick here, but the last paycheck you gave me bounced and....
Robotnik: Not now Snively! This robot needs a power source, go outside and catch me a squirrel.
Snively: Wait what? We have some power cells here I can just...
Robotnik: Snively get your head out of your ass. Have you seen energy costs lately? Fucking oil prices have been going through the roof. But there's squirrels and mice and birds and shit everywhere. The perfect renewable energy source.
And thus were the beginnings of the 'varmit reactor' technology Robotnik would come to master. Interesting side note, this technology is currently being pursued very aggressively by Solyndra. Robotnik would expand this process of shoving a small animal into a robot, or 'Robotisizing' as he calls it, into a stream lined process used to turn enemies into robot slaves. Most recently he robotisized Princess Sally turning her into a super weapon and, many suspect, his own personal sex robot.
But why use this technology for evil? Surely he could have made his world a better place with his genius? Perhaps some childhood trauma haunts him. Perhaps he is jealous of his cousin Jamie's lucrative job co-hosting Mythbusters. Or perhaps, as many speculate, Robotnik is just a dick. Seeing as how the last therapist to attempt to treat Dr. Robotnik was turned into a robot penguin, the world may never know.