Yeah, you can't just arrive at a million-dollar idea like "a hedgehog who runs really fast" without going through a bunch of shitty ones first. When Sega first decided to introduce a new mascot who would defy Nintendo's supremacy, their early proposals included a dog, a clown, and a bizarre Mario/Bart Simpson hybrid ...
"Don't have a mushroom, man!"
... before they settled on the most hardcore of animals, the rabbit. The only problem: Their 16-bit console just couldn't handle the sheer coolness (or hardware demands) of the rabbit's ears, which were supposed to allow him to grab hold of things. Hell, this was 1991 -- it'd probably take a room full of MIT computers to make that happen, and that was a little more than you could pack in a $299 box. So, no rabbits.
After being an armadillo for a while, Sonic (or "Mr. Needlemouse") finally became a hedgehog. With an appetite for bestiality. In a concept that was later rejected by Sega of America for being too "Japanese," the developers decided to give Sonic a sexy human girlfriend named Madonna who would chase him around, implying that she wanted to do unspeakable things with his spiky member.
Yes, all concept art is indistinguishable from the bad Sonic drawings you did in middle school.