The Kintobor name was never used in the games. Only "Robotnik" was given outside of Japan. Other continueties used "Kintobor" in explaining how Dr. Robotnik (Eggman) became evil, saying that he reversed his name when he changed. Since the games are now trying to move back to the Japanese names, they made "Robotnik" the last name of Gerald and Maria, as though it's Eggman's family name.
~ Crazy C Lea