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 B. Lewis, identified genes that control the segmentation pattern of the "Drosophila" embryos. The "hh" loss of function mutant phenotype causes the embryos to be covered with denticles, small pointy projections resembling the spines of a hedgehog. Investigations aimed at finding a "hedgehog" equivalent in vertebrates by Philip Ingham, Andrew P. McMahon, and Clifford Tabin, revealed three homologous genes. Two of these, "desert hedgehog" and "Indian hedgehog", were named for species of hedgehogs, while "sonic hedgehog" was named after Sonic the Hedgehog, the protagonist of the eponymous video game franchise. The name was devised by Robert Riddle, who was a