The series has introduced dozens of additional recurring characters over the years. All five of these have remained major characters and appeared in dozens of games. Sonic 3 introduced Knuckles the Echidna, Sonic's rival and, later, friend. Sonic CD introduced Amy Rose, a female hedgehog with a persistent crush on Sonic. The sequel, Sonic 2, gave Sonic a fox friend named Tails. 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). Clockwise from top: Doctor Eggman, Rouge the Bat, Shadow the Hedgehog, Knuckles the Echidna, Sonic the Hedgehog, Amy Rose, Miles "Tails" Prower, Cream the Rabbit, a Chao, and Blaze the Cat.