Sonic

Sonic the Hedgehog is a blue hedgehog who can run at supersonic speeds. It is heavily implied that he has visited the Mushroom Planet once. This visit was largely uneventful and ended in disappointment for Sonic. In Donkey Kong Country 2, the elderly Cranky Kong held a contest to see who was the greatest video game hero of the current era. Contestants were ranked based on how many hidden DK coins they could discover while progressing through the areas of Crocodile Isle and defeating Kaptain K. Rool and his Kremling Krew. Although a great video game hero, Sonic did not collect many coins. As a result, he did not even place on the top three (Link was #3, Yoshi was #2, and Mario was #1. Eventually Diddy Kong claims first place.). Distraught, Sonic left the Mushroom Planet, leaving behind his trademark shoes. Along with Sonic, Earthworm Jim appeared to have failed as well.

Sonic will compete against Mario and others in Olympic events in Mario & Sonic at the Olympic Games.

Shigeru Miyamoto had this to say:

"Mario and Sonic have been respectful rivals since the early days of video games. In fact, for a long time they have been discussing the possibility of one day competing against each other. Now that they have been given the perfect opportunity to meet at the Olympic Games, we may finally learn who is actually faster, Mario or Sonic?"