Harmonix and RedOctane's Guitar Hero shipped with a plastic guitar controller and a tracklist of rock classics, and suddenly millions of people were shredding solos in their living rooms. The five-button fret system was simple enough for beginners but scaled into genuinely demanding gameplay at expert difficulty. Guitar Hero II and III became cultural juggernauts, moving millions of units and reviving interest in classic rock songs. Aerosmith reportedly earned more from Guitar Hero: Aerosmith than from any single album they ever released.