In 2016, the Head of the Sonic Team, Takashi Iizuka said, “when the game was originally developed in Japan, they called the character Eggman”, he told Game Informer. “That was the name of the character, but when the game got localized and ported into the Sonic the Hedgehog that we know in the West, they decided to without confirming with the development team, change his name to Ivo Robotnik or just Robotnik. That’s kind of when everyone first learned about the character. Of course, this was without consulting the people who made the game. They just kind of went off and did it.”
This led to a problem when the game was released in Japan on July 26, 1991, the instruction book listed him as Doctor Eggman. So now they had the same character with two different names. Arguably the US version was released first, but internally the US team never said that as the official name. The names created so much confusion that Sega had to unify everything in 1999 with Sonic Adventure where he’s referring to as both Robotnik and Eggman.
Yuji Naka one of the original Sonic creators tried to find a solution to the problem in 2008. “To tell the truth, his name has not changed said Naka.” “Robotnik is his real name and Eggman is a common name taken after his shape.”
What About The Movie?
In the Sonic the Hedgehog movie, Jim Carrey’s mustacheoid villain is called Dr. Ivo Robotnik. But in an imposition moment, James Marsden’s character calls him “Eggman” as an insult. This actually follows closely with what Sega has presented as the answer to the debate. In short, Dr. Ivo Robotnik if you’re inviting him to dinner and “Eggman” if you’re kicking him out of your house.