These days the former is a nickname
The early days of the wild west of localization are a fascinating beast.
We’ve seen it with series like Final Fight and Mario, but one that isn’t mentioned that often is Sonic — particularly when it comes to the main villain’s moniker. That’s mainly because the Japanese original of “Eggman” and the western “Robotnik” have been used either interchangeably or simultaneously, and Sonic Team head Takashi Iizuka once again has stepped in to clarify the situation.
Speaking to Game Informer, Iizuka notes that as we all know, the original developers in Japan called him “Eggman,” and that was the end of it. But when the game was localized, the western team “without consulting” with the team overseas, changed it to “Ivo Robotnik.” Over time after Sonic gained popularity Sega wanted to unify the name, which was an effort spearheaded by Iizuka. He explains how in Sonic Adventure he combined the two, creating Dr. Ivo “Eggman” Robotnik as canon.
There’s a few more good bits in there like why Tails is invulnerable, the current state of the Chao species, and why Sonic has recently been sporting scarves. It’s nothing too revealing outside of the aforementioned name battle, but it’s nice to see that Iizuka is still passionate about the series.
Sonic The Hedgehog Burning Questions Finally Answered [Game Informer]