Eggman and Robotnik are the same guy. "Eggman" is just a nickname, though, in America. In Japan (where the whole Sonic series started), though, "Eggman" was his name. America decided to follow suit, from Sonic Adventure onward, using "Robotnik" as his official name, but being called "Eggman" by himself and the Sonic heroes.
It may be that Japan has adopted the "Robotnik" thing from America, and did exactly what we did: Use the name as official, but make "Eggman" a nickname.
no one out-awesomes me! i'd kill... uhhhh... Toad, because no one cares about Toad! (stated in Super Mario Logan's videos. ps. Super Mario Logan on youtube is awesome! even though im a huge sonic fan...!)
Minecraft Clan: Swordmasters of Hyrule / Skype: thesupersonic233