Over the last 15 years or so, Sonic and friends have gone through many different changes, especially eggman, or robotnik to some. From what I can remember, he has gone over five different look in his lifetime. Below are some info about each one.:
Robotnik/Eggman Classic: (appeared in Sonic, 2 & 3, etc.) This was the original eggman/robotnik who wanted to take over the world by capturing small animals and turning them into his robotic slave. Every time he tries something, Sonic would always stop him.
Robotnik SATAM: (appeared in Sonic TV series SATAM & Sonic Underground, Sonic comics) Like eggman/robotnik classic, he would capture small animals and turn them into his robotic slaves, but this time with a darker tone to it or something. Given a different look to fit the american audience at the time, he was all about pollution and world conquest.
Robotnik AOSTH (appeared in Sonic TV series AOSTH and Dr. Robotnik's Mean Beam Machine) In the show, he's really a joke compare to the other eggmans/robotniks. Taking a more fatter and cartoonish look than the other one, he still care about pollution. He was more of a comedic character than the serious character from SATAM
Robotnik/Eggman Current (appeared in Sonic Adventure 1 & 2, Sonic Advance, etc.) A more taller Eggman/Robotnik, he's pretty much all about world conquest than animal capture these days. At some points of the games, he would team up with Sonic and fixed the problem that he caused.
Eggman Next-Gen (appeared in Sonic the Hedgehog 2006) Haven't played Sonic Next-Gen, so I don't know if he's the same as Eggman/Robotnik Current or what.
(If my facts are incorrect, fix it for the other users; if this has been done before, lock it or something)
So after all of this, it's time for the question. So NG users.........