Sonic the Hedgehog protagonist Sonic the Hedgehog, a blue hedgehog able to run at supersonic speeds, and recurring villain Dr. Eggman, an evil scientist whose ambition is to conquer the world. Among Sonic's many allies, the most well-known include: Miles "Tails" Prower, a twin-tailed, highly intelligent yellow fox who is Sonic's sidekick and best friend; Amy Rose, a pink hedgehog who is Sonic's self-proclaimed girlfriend and a hero in her own right; Knuckles the Echidna, a coolheaded red echidna who is the guardian of the Master Emerald; Shadow the Hedgehog, an anti-heroic doppelgänger of Sonic with a dark past; and Metal Sonic, a
Sonic the Hedgehog was built on a more advanced version of the engine used for "Sonic Heroes". It focused on Shadow the Hedgehog as he tried to uncover his past. The game contained multiple paths and endings, as the player chose to take good or evil paths for each level. It also added wielding weapons and driving vehicles to 3D platforming. "Sonic Riders" was the first "Sonic" racing game since "Sonic R"; in contrast to the previous game, the characters used hoverboards, bikes, and skates rather than racing on foot. It was the last game for GameCube & Xbox. Due to the extended