Naming variations
Eggman has been known by several names. In the Japanese games, he has always been known simply as "Dr. Eggman". In all games released in America and Europe up to Sonic Adventure, however, he was known as "Dr. Robotnik".
Both names slipped occasionally in all regions. For example, Sonic the Hedgehog 2's Wing Fortress Zone and Sonic Drift 2 only had Eggman, Sonic Triple Trouble had a stage called Robotnik Winter Zone, and Sonic Jam had both names, as his profile was Robotnik and his statue next to Sonic said Eggman on it. In one episode of the American animated series Adventures of Sonic the Hedgehog Tails said "Guess again EGGMAN!" to Robotnik. This was probably meant as an insult, given his round physique, but it could also have been a Sega in-joke.
In Sonic Adventure, however, Sega began a process of getting the American and European gaming communities to use the Japanese name. Initially, both names were used, and he referred to himself as Robotnik while others called him "Eggman". In the sequel, Sonic Adventure 2, when he is announcing that he is taking over the world, he refers himself as Dr. "Eggman", but in the background are the words "Robotnik Empire". In later games, and also in the English dub of Sonic X, the name Robotnik was dropped almost entirely, though it can still be found on some promotional material and in the French Sonic X dub. In the Japanese version of Sonic X his eyecatch profile card gives his name as: "ROBOTNIK (Dr. Eggman)". Also, most airboards in the game Sonic Riders were built by Robotnik Corp.
In the SatAM cartoon and Archie Comics, his first name is Julian, with his full name in the Archie Comics being 'Julian Kintobor of the house of Ivo'. Kintobor is also the surname used by all his known relatives in the comic save for those from Sonic Adventure 2 (see below), as his nephew and niece (Snively and Hope, respectively) both have the last name Kintobor, itself being 'Robotnik' spelled backwards.
General consensus now is that his surname is Robotnik (which is different from his official name), and his official name is Eggman [4] [5] [6]. This is supported by the surnames of his relatives, Gerald Robotnik and Maria Robotnik.
According to "Sonic Channel", the official Japanese Sonic website, Eggman is a nickname and his true name is listed as "unknown". [1]