For 17 years, Willis was an essential component of Frank Zappa's music: as lead singer and rhythm guitarist, joining Zappa on six world tours, and appearing on no less than 30 of Zappa's official releases (most recently the posthumous Trance-Fusion and Buffalo) until Zappa's death from prostate cancer in 1993. Since that time he as toured, performed and/or recorded with: The Muffin Men, Banned From Utopia, Project/Object, Ed Palermo, The Central Scrutinizer, Ossi Duri, Cuccurullo Brillo Brullo and others.