His death was confirmed by Bernard MacMahon of Lo-Max Records in London, which released his most recent album, “The Unfairground,” in 2007.

Mr. Ayers was a young misfit in Canterbury in the 1960s, with long hair (he would later become fond of eye makeup), arty interests and few friends, when he connected with the musicians, including the drummer and singer Robert Wyatt, with whom he would eventually form the influential band Soft Machine. The band’s first single, “Love Makes Sweet Music,” was released in 1967.

Mr. Ayers, who sang and played electric bass and guitar, wrote songs that could be jazzy, playful or dense, with unusual instrumentation, brooding choruses or spoken lyrics that may or may not have been intended as meaningful. He sang in a melancholy baritone, with clean diction.

“Why Are We Sleeping?,” which he wrote with two other members of the band, for the first Soft Machine album, starts:

It begins with a blessing, it ends with a curse

Making life easy by making it worse

“My mask is my master,” the trumpeter weeps

But his voice is so weak, as he speaks from his sleep

Saying: “Why, why, why, why are we sleeping?"

Authorities on British rock regarded Soft Machine and Mr. Ayers as crucial influences on the avant-garde music that developed in the late 1960s, including the psychedelia of Jimi Hendrix (who gave Mr. Ayers a guitar) and Pink Floyd. Mr. Ayers recorded at least one session with Pink Floyd’s early leader, Syd Barrett.

Soft Machine toured the United States as an opening act for Hendrix in 1968, but Mr. Ayers left the band soon afterward to live on an island off the coast of Spain.

Departure became something of a pattern for him. Just as he would near commercial success, or simply stability, he would display his lack of interest by disappearing. But he kept making music, including solo records throughout the 1970s that were critically acclaimed and beloved by his fans. Those efforts included “Joy of a Toy,” “Bananamour” and “The Confessions of Dr. Dream and Other Stories.”

There would be longer and longer stretches before Mr. Ayers emerged from his Mediterranean beach life. He struggled with drugs and drank heavily, and he was not afraid to mingle with the wives of other musicians. In a 2008 interview with Word magazine, Mr. Ayers said he saw little merit in ambition.

“Honestly, I just assume that whatever is going to happen to me is going to happen,” he said. “There it goes: someone is there, someone isn’t there. This girl is here. This food is here. I think the clever people are the ones who do as little as possible.”

Mr. Ayers was born on Aug. 16, 1944, in Herne Bay, Kent, England. His father, Rowan Ayers, was a BBC producer who helped create “The Old Grey Whistle Test,” a late-night television show that focused on artistically ambitious rock music.

Mr. Ayers’s parents divorced when he was very young, and he spent many of his early years with his mother and her new husband in Malaysia. He returned to England at about 12 and eventually met Mr. Wyatt and Mike Ratledge, another early bandmate. He said in the Word interview that those friendships were “the first experience of intimacy, the first family I ever had.”

His survivors include three daughters, Rachel Ayers, Galen Ayers and Annaliese Ellidge, and a sister.

It had been 15 years since Mr. Ayers released a recording when, in 2007, Lo-Max asked him to make an album based on some home recordings a friend of his had surreptitiously shared with the label. Mr. Ayers needed to be coaxed into doing it.

“He didn’t have any desire to make a big public statement, really,” Mr. MacMahon said. “His main concern was, were the songs good enough to be recorded? I got the impression that he did it for the satisfaction of doing something he was proud of.”