Naoto Ohshima's first character design for Dr. Robotnik/Dr. Eggman was a fat, mustachioed man in pajamas. According to Yuji Naka, Ohshima made him rotund as part of their overall design philosophy to "create something easy enough so that kids would be able to draw the characters." While many have noted that this early design bears a resemblance to former United States president Theodore Roosevelt, Ohshima denied that he was meant to be based on Roosevelt in 2018, and believed the design was subconsciously influenced by a variety of characters he had seen before. Some have theorized that his inspiration was taken from a recurring character design seen in some works by animation director Hayao Miyazaki, including an episode of the 1979 anime series "Lupin the 3rd Part 2" (which Ohshima is a professed fan of), the 1986 film "Castle in the Sky", and later in the 2003 film "Spirited Away".