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 hedgehog postdoctoral fellow at the Tabin Lab, after he saw a Sonic comic his daughter had brought from England. In the zebrafish, two of the three vertebrate "hh" genes are duplicated: "SHH a", "SHH b" (formerly described as "tiggywinkle hedgehog", named for Mrs. Tiggy-Winkle, a character from Beatrix Potter's books for children), "ihha" and "ihhb" (formerly described as "echidna hedgehog", named for the spiny anteater and not for the echidna character Knuckles in the "Sonic" franchise). Of the "hh" homologues, "SHH" has been found to have the most critical roles in development, acting as a morphogen involved in patterning many systems,