Mars Williams (born May 29, 1955) is an American jazz and rock saxophonist. Exposed to big band and dixieland jazz by his trumpet-playing father, Williams played classical clarinet for ten years, then migrated to saxophone in his last year of high school, citing the influence of Eric Dolphy, John Coltrane, and Charlie Parker. He attended De Paul University and later the Association for the Advancement of Creative Musicians where he studied under founders Anthony Braxton and Roscoe Mitchell. In 2004 he was selected by the Moers Festival as their featured artist.
Williams is a musician, orchestrator, and arranger who has played with The Waitresses and The Psychedelic Furs. He was only to tour with The Furs in Australia for a month in 1983 as then sax-player Gary Windo was unable to make the trip. After a successful tour and the breakup of the Waitresses, he was asked to stay on as a permanent member, which he did until 1989 and later rejoined in 2005. He has also performed with Billy Idol, the Power Station, Billy Squier, Massacre, Ministry, and Die Warzau and the Ike Reilly Assassination.
He has toured and recorded with the Peter Brötzmann Tentet, the Vandermark 5, Cinghiale, Our Daughter's Wedding, and Mark Freeland's Electroman, and is the bandleader of several spin-off jazz groups: Grammy Award nominated, acid jazz pioneer Liquid Soul, Hal Russell's NRG Ensemble, Witches & Devils, Slam, and XmarsX. He is active in the Chicago improvisational jazz underground scene both individually and as a member of the quartet Extraordinary Popular Delusions.