Rock Band was the rival music-game series Harmonix created after leaving Guitar Hero. The first Rock Band was released in 2007 by Harmonix and MTV Games, building on the note-matching ideas Harmonix had developed for Guitar Hero.
Unlike the original Guitar Hero games, which centered on a guitar-shaped controller, Rock Band was designed around a full group. Players could perform guitar, bass, drums, and vocals, allowing several people to simulate playing together. This broader setup helped distinguish it from its former series.
Harmonix had already developed the first Guitar Hero and Guitar Hero II before MTV Games acquired the studio in 2006. Because Harmonix was no longer making future Guitar Hero games, Activision moved main-series development to Neversoft.
Rock Band also treated the game as an ongoing music platform. Its downloadable-song program let players expand their libraries without buying an entirely new disc, an approach that became a major part of the series. Dance Central was another Harmonix franchise, but Rock Band is the direct Guitar Hero rival asked about here.