Sonic the Hedgehog 3 is a 1994 platform game developed and published by Sega. Like previous Sonic games, players traverse side-scrolling levels at high speeds while collecting rings and defeating enemies. They control Sonic and Tails, who attempt to retrieve the Chaos Emeralds to stop the evil Doctor Robotnik (Dr. Eggman) from relaunching his space station, the Death Egg, after it crash-lands on a mysterious floating island. Sonic 3 introduces Knuckles the Echidna, the island guardian, who lays traps for Sonic and Tails. Development began in January 1993 by Sega Technical Institute (STI) in California, shortly after the release of Sonic the Hedgehog 2. It was initially developed as an isometric game similar to Sonic 3D Blast (1996), but became a conventional 2D platform game due to time constraints. Sonic 3 was developed simultaneously with Sonic & Knuckles; they were planned as a single game until time constraints and cartridge costs forced the developers to split it. The Sonic 3 cartridge can be attached to an adapter on the Sonic & Knuckles cartridge, creating a combined game, Sonic 3 & Knuckles. According to some members of the development team, pop musician Michael Jackson composed portions of the soundtrack but left the project and went uncredited; his involvement was denied by senior Sega staff. Sonic 3 was released for the Sega Genesis in North America and Europe in February 1994, and in Japan in May. As with its predecessors, it was a critical and commercial success, with critics seeing it as an improvement over previous installments. It sold over one million copies in the United States, making it one of the bestselling Genesis games. It has been rereleased for various platforms, including as part of the compilations Sonic Jam (1997), Sonic & Knuckles Collection (1997), Sonic Mega Collection (2002) and Sonic's Ultimate Genesis Collection (2009).