<P> The Sonic the Hedgehog video game franchise began in 1991 with the game Sonic the Hedgehog for the Sega Genesis, which pitted a blue anthropomorphic hedgehog named Sonic against a rotund male human villain named Doctor Eggman (or Doctor Ivo Robotnik). The sequel, Sonic 2, gave Sonic a fox friend named Tails . Shortly afterward, Sonic CD introduced Amy Rose, a female hedgehog with a persistent crush on Sonic, and Sonic 3 introduced Knuckles the Echidna, Sonic's rival and, later, friend . All five of these have remained major characters and appeared in dozens of games . </P> <P> The series has introduced dozens of additional recurring characters over the years . These have ranged from anthropomorphic animal characters like Shadow the Hedgehog and Cream the Rabbit to robots created by Eggman like Metal Sonic and E-123 Omega, as well as human characters like Eggman's grandfather Gerald Robotnik . The series also features two fictional species: Chao, which have usually functioned as digital pets and minor gameplay and plot elements, and more recently, Wisps, which have been used as power - ups . </P>

What is sonic the hedgehog's friends name