Muir, who has died aged 79, was introduced to the public in late 1972 as a member of King Crimson. This was the third lineup convened by the group’s leader, the guitarist Robert Fripp, under a name that had first made headlines in 1969 with an appearance at the Rolling Stones’ free concert in Hyde Park, followed by the release of an incendiary and globally successful debut album.

Fripp’s new assemblage included the singer and bassist John Wetton, the young violinist David Cross, and a drummer, Bill Bruford, whom he had enticed away from Yes, another successful progressive rock group.

In the six months Muir stayed with them, his presence changed the group’s philosophy completely, loosening the notoriously strict guidelines imposed by Fripp and exploring the boundaries of improvisation.

This was a shock not just for their audiences but for the musicians, too. Into Fripp’s world of complex interlocking riffs in unorthodox time-signatures came a man in a bearskin bolero, orange loon pants, a waxed moustache, an infectious grin and an instinct for disruption, whose idea of a solo might involve emptying a sack of leaves over his kit.

For Bruford, a schooled musician for whom the experience might easily have been discomfiting, Muir’s presence – almost that of a performance artist – represented a liberation. “He had a volcanic effect on me,” he remembered.

But then, suddenly, on the eve of a tour of the UK, Europe and the US, he was gone. The group’s management issued a statement claiming that his absence was caused by an injury suffered on stage. In fact Muir had returned to  https://www.theguardian.com/uk/scotland" rel="nofollow - Scotland  to spend several years as a Buddhist monk, the indulgences of his former life replaced by retreat and meditation. Later he returned to painting, to which he devoted the decades before his death.

Born in  https://www.theguardian.com/uk/edinburgh" rel="nofollow - Edinburgh , one of the four children of a solicitor, William Gray Muir, and his wife Elizabeth (nee Montgomery), he attended Gordonstoun school in Moray, where he encountered a younger pupil who would become King Charles III. That was followed by Edinburgh College of Art, where he studied painting while playing the trombone in jazz bands.

In 1967, having dropped out of college and switched to drums, he joined a free-jazz group called the Assassination Weapon, who played in a pub with their own light show until attracting the attention of the police and losing the gig “for inducing a drug-like atmosphere”.

Moving to London, he took a job as a department store assistant while playing with various bands, including the poet/singer Pete Brown’s Battered Ornaments, the jazz-rock band Sunship and the Afro-rock band Assegai.

He also founded a short-lived free-improvisation group called Heavy African Envelope, two of whose members, the singer Christine Jeffrey and the electronicist Hugh Davies, would also join him, along with the saxophonist Evan Parker and the guitarist  https://www.theguardian.com/news/2005/dec/31/guardianobituaries.artsobituaries" rel="nofollow - Derek Bailey , in the Music Improvisation Company, which made an album for the ECM label in 1970.

That year he joined the saxophonist  https://www.theguardian.com/music/2020/jun/09/don-weller-obituary" rel="nofollow - Don Weller  in a four-piece rock band called Boris, whose appearance at the Marquee in London received an enthusiastic recommendation in Melody Maker. Intrigued by that review, and by a subsequent interview Muir gave to the paper, Fripp contacted him. After the two had played together informally, the drummer became a most unlikely recruit to the guitarist’s new lineup.

Their first full appearance was on a popular weekly German TV show called Beat Club Bremen, followed by a 27-date tour of the UK, where audiences were disconcerted to find that the only tune they recognised was  https://www.youtube.com/watch?v=7OvW8Z7kiws" rel="nofollow - 21st Century Schizoid Man , a favourite from the first album, itself withheld until the encores.

When the band made a studio album, Larks’ Tongues in Aspic, its title was taken from the phrase Muir produced in response to a request to describe the kind of music they were now playing.

“King Crimson was ideal for me because it was a rock band with more than three brain cells,” Muir said later. “I felt completely at home.” Reviewers and audiences, once they had recovered from the initial shock, were largely enthusiastic. Nevertheless, after a gig at the Marquee his colleagues learned of his decision to leave not just the band but the world of music with immediate effect.

He had been persuaded to lead a different life by reading Autobiography of a Yogi, by Paramahansa Yogananda. “I didn’t feel happy about letting people down,” he said, “but this was something I had to do or else it would have been a source of deep regret for the rest of my life.” His next few years were spent at the Samye Ling monastery near Eskdalemuir in Dumfries and Galloway.

When Muir re-emerged in the early 80s there were occasional engagements with music, including a duo album, Dart Drug (1981), with Bailey, and the soundtrack to a film called Ghost Dance (1983). But painting became the priority, first in Islington, north London, and then at a permanent home near Penzance in Cornwall, although exhibiting his work held little interest for him.

Parker remembers Muir asking him to sit for his portrait, and taking a long time over doing so, using a pencil to produce a work in a very detailed and painstaking hyper-realist style. When it was finished, Muir laid it on his kitchen floor over a sprinkling of leaves and rubbed the pencil across the paper to produce a frottage effect before picking it up, showing it to Parker, crumpling it into a ball and tossing it into a waste bin.

He is survived by his brother, George, and a sister, Mary. Another brother, Andrew, predeceased him.