The Guitar Hero series (sometimes referred to as the Hero series) is a series of music rhythm games first published in 2005 by RedOctane and Harmonix, and distributed by Activision, in which players use a guitar-shaped game controller to simulate playing lead, bass guitar, and rhythm guitar across numerous rock music songs. Players match notes that scroll on-screen to colored fret buttons on the controller, strumming the controller in time to the music in order to score points, and keep the virtual audience excited. The games attempt to mimic many features of playing a real guitar, including the use of fast-fingering hammer-ons and pull-offs and the use of the whammy bar to alter the pitch of notes. Most games support single player modes, typically a Career mode to play through all the songs in the game, and both competitive and cooperative multiplayer modes. With the introduction of Guitar Hero World Tour in 2008, the game includes support for a four-player band including vocals and drums. The series initially used mostly cover versions of songs created by WaveGroup Sound, but most recent titles feature soundtracks that are fully master recordings, and in some cases, special re-recordings, of the songs. Later titles in the series feature support for downloadable content in the form of new songs.