He made his name in the 1980s with the Waitresses and the Psychedelic Furs, but his roots were in the exploratory jazz of Eric Dolphy and Ornette Coleman.Weakened by surgery to remove a tumor near his pancreas in January, followed by six months of chemotherapy, the high-wattage saxophonist Mars Williams learned this past summer that his treatment options were nearly exhausted.But rather than resting an ailing body, he chose to return to the road. He joined the Psychedelic Furs, a band he had performed and recorded with since the 1980s, as it toured the United States.“Being on a grueling bus tour would be exhausting for anyone,” Dave Rempis, a friend and fellow saxophonist, said in a phone interview. “By the end, he was sitting in a dressing room with blankets and heaters all around him. He could barely move. But he would still go out onstage and play as hard as ever. He just wanted to be back onstage where he felt most alive.”Mr. Williams died at a hospice facility in Chicago on Nov. 20. He was 68. His brother, Paul R. Williams, said the cause was ampullary cancer.Mr. Williams was angling for a career in jazz in 1981 when the Waitresses, an idiosyncratic New York-based new wave band, came calling, dangling a newly minted record deal with Polydor. The band, marked by the deadpan vocal stylings of Patty Donahue, scored with the indelible cult hits “I Know What Boys Like” and “Christmas Wrapping,” as well as the theme song to the celebrated, if short-lived, 1980s high school sitcom “Square Pegs.”With his explosive horn lines and electric stage presence, Mr. Williams captured the spirit of the band — never mind that his grounding in the exploratory jazz of Eric Dolphy and Ornette Coleman made him an odd fit in the milieu of MTV in its early days, when acts could find overnight fame on the strength of cotton-candy haircuts and passable synthesizer skills.“He was a goofball, like a lot of reed players,” Chris Butler, the Waitresses’ founder and chief songwriter, said in a phone interview. “I think it has something to do with all that back pressure on their brains when they’re blowing into a brass tube, you know. But he had such massive chops. When we played live, he would improvise, solo, fill the arrangements with this magnificent stuff. And it was different every night.”No instrument, it seemed, was off limits to Mr. Williams, including bells, whistles, and pots and pans. “I had a lot of freedom,” he said in a 2019 interview with the jazz journalist Howard Mandel. “I’m up blowing Tibetan monk horn solos over their rhythms. I’m able to do all these different styles within this pop band.”From left, Tracy Wormworth, Patty Donahue, Dan Klayman and Mr. Williams of the Waitresses at the Peppermint Lounge in New York in 1981, the year Mr. Williams joined the band. Michael Macioce/Getty ImagesHe joined the Psychedelic Furs, a British post-punk band, after the Waitresses fragmented in 1983. His new group was then trading its early Velvet Underground-style rawness for a slicker brand of pop following the success of alternative hits like “Love My Way” (1982).Mr. Williams lent his wailing horn lines to the band’s 1984 album, “Mirror Moves,” although he was not featured on the album’s sleeve or in the heavily aired videos for its songs “Heaven” and “The Ghost in You.” He toured and recorded with the Psychedelic Furs until 1989. After a long hiatus, he rejoined them in 2005.Ever the musical explorer, Mr. Williams performed with many rock and pop acts, including the Killers, Billy Idol and Jerry Garcia, and earned acclaim with several Chicago jazz outfits, including his own long-running ensemble, Liquid Soul, which performed at inauguration festivities for President Bill Clinton in 1997 and earned a Grammy Award nomination for its 2000 album, “Here’s the Deal.”“Mars Williams is one of the true saxophone players — someone who takes pleasure in the sheer act of blowing the horn,” the avant-garde jazz saxophonist and composer John Zorn wrote in the liner notes to “Eftsoons,” Mr. Williams’s 1981 collaboration with the jazz composer and bandleader Hal Russell, “and there are not many saxophone players I can truthfully say this about.”Marc Charles Williams was born on May 29, 1955, in Elmhurst, Ill., the fifth of six children of Jack Williams, who owned several pharmacies and served as an Illinois state representative, and Hilda (Van Outrive) Williams, who managed the Cook County ethics department. He picked up his nickname from a mispronunciation of his first name by his baby brother, Paul.In addition to his brother, his survivors include his mother and two sisters, Michele Williams-Piotrowski and Suzy Williams. His sister Valerie Williams and his brother Jack died.A classically trained clarinetist as a youth, Mr. Williams switched to saxophone after graduating from Holy Cross High School in River Grove, Ill., in 1973 and briefly studied music theory at DePaul University in Chicago.His musical journey led him to New York City, where he worked as a bike messenger and played gigs with punk bands at the nightclub CBGB while trying to build a career in jazz before taking a detour into pop that would last until his final months.Once his pop career took off, life on the road came with familiar perils, including drug addiction, which he wrestled with for years. He spent his last two decades sober, he said in interviews, while counseling other musicians in their struggles.Mr. Rempis said he last saw Mr. Williams on Oct. 25.“He had gotten back from six weeks on the road with the Psychedelic Furs,” he said, “and ended up in the hospital for a few days. When he got out, he said, ‘You know, I might not be able to do these tours in December in Europe.’ That’s where his head was at: Where am I going now? What’s the next thing?” More