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?"

Trivia

 * Nintendo was once business rivals with Sonic's company of creation, Sega; this rivalry peaked during the 16-bit area. As such, Nintendo and Sega often attempted to put each other down through their games (thus explaining Sonic's humiliation in Donkey Kong Country 2 and possibly explaining the blue hedgehog enemies of Super Mario World 2: Yoshi's Island), and Sega did so a notably large amount of times more than Nintendo. Examples of Mario mockeries in Sonic the Hedgehog series forms of media include the emphasis on "Super" on the back of Sonic the Hedgehog ' s box (a reference to Super Mario Bros. and other Mario series titles beginning with "Super") and the Marxio Brothers of Sonic the Comic, a British comic book about Sonic and his friends.
 * An April Fool's Day issue of the magazine Electronic Gaming Monthly once said that Sonic and his friend Tails were unlockable Super Smash Bros. Melee; however, this was soon proved to be a hoax.