The following snippets come from a classic interview with Yuji Naka, in which he discusses the creation of Sonic the Hedgehog. First up, he talks about how Sonic's original design was a rabbit.
I wrote up a memo that was basically a “next game I want to make” list, and showed it to my boss. But the one that caught his attention was the very last entry on the list, which said “an action game to challenge Mario”. (laughs) I tried to object, saying “Actually, I wrote them in order of which ones I want to do…” but he didn’t listen to me at all. (laughs) So we got started on the Sonic the Hedgehog development, with 3 or 4 members. In the beginning it was just a program where you moved a ball-like object around, then at some point it was a rabbit...but something felt very off about it. And ultimately we decided to give the character a somersault attack.
That idea actually came from a notebook I had in high school, scribbled there on the very last page. I figured I would use it when I quit Sega and went independent, but as we were making Sonic it was like, “well, I’ve got no choice, I guess I’ll have to use it now.” However, if a rabbit does a somersault attack, it’s just going to hurt itself, right? We thought it would be better to have some animal with a hard shell or spines. Two possibilities came up: an armadillo or a hedgehog, but the hedgehog won out because it was faster.
Naka also went on to discuss how the Super Mario Bros. series was a jumping point for what Sonic games would focus on.
I think Super Mario Bros. is a wonderful game, but if you play it everyday, you always have to start from stage 1-1, right? Once you get good and memorize the levels, you can just hold down the B button and run through the stage. But even then it just takes too long. With Sonic, I wanted to shorten that time if I could. My idea was that you’d progress slowly and carefully through the stages on your first playthroughs as you learned the enemy locations, but after you got used to it, you could really zoom straight through the levels. Unfortunately, everyone who playtested it just went full-speed from the very beginning. (laughs)