Reasons for why Dr. Robotnik's nickname is Eggman

 Dr. Robotnik, is a evil genius. People over the years started calling him Eggman. Why? I'll tell you right here...

Robotnik and Eggman are both fitting, but Eggman describes more of Robotnik in 1 word.

1. The egg in Eggman stands for that he is a egghead and he is shaped like a egg.

2. Robotnik only explains that he is obsessed and fed up about robots and machines; Eggman explains more.

3. You don't need to write the "Dr" in his name.

4. In The Adventures of Sonic The Hedgehog, Sonic liked calling Eggman, egg belly, which explains a lot of the name, Eggman.

And that's four reasons why his nickname is Eggman.