Sonic the Hedgehog is a Japanese video game series and media franchise created and owned by Sega. The franchise follows Sonic, an anthropomorphic blue hedgehog who battles the evil Doctor Eggman, a mad scientist. The main Sonic the Hedgehog games are platformers mostly developed by Sonic Team; other games, developed by various studios, include spin-offs in the racing, fighting, party and sports genres. The franchise also incorporates printed media, animations, feature films, and merchandise.

Sega developed the first Sonic game, released in 1991 for the Sega Genesis, to compete with Nintendo’s mascot Mario. Its success helped Sega become one of the leading video game companies during the fourth generation of video game consoles in the early 1990s. Sega Technical Institute developed the next three Sonic games, plus the spin-off Sonic Spinball (1993). After a hiatus during the unsuccessful Saturn era, the first major 3D Sonic game, Sonic Adventure, was released in 1998 for the Dreamcast. Sega exited the console market and shifted to third-party development in 2001, continuing the series on Nintendo, Xbox, and PlayStation systems.