A Perfect Circle is an American rock supergroup formed in 1999 by guitarist Billy Howerdel and Tool vocalist Maynard James Keenan. A Perfect Circle has released four studio albums, the first three during the early 2000s: Mer de Noms, their debut album in 2000, and followed up by Thirteenth Step in 2003; then in 2004, Emotive—an album of radically re-worked cover songs.