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 (character) "Sonic & Knuckles", both released in 1994, saw Sonic and Tails battle Robotnik again, with the additional threat of Knuckles, who is tricked by Robotnik into thinking Sonic is a threat. "" (2010–2012) continues where the story of "Sonic 3" left off, reducing Sonic to the only playable character and releasing in episodic installments. The second episode sees the return of both Tails as Sonic's sidekick and Metal Sonic as a recurring enemy. Other two-dimensional platformers starring Sonic include "Sonic Chaos" (1993), "Sonic Triple Trouble" (1994), "Sonic Blast" (1996), "Sonic the Hedgehog Pocket Adventure" (1999), "Sonic Advance" (2001), "Sonic Advance