An American bass guitarist and recording engineer best known for his involvement in various psychedelic rock bands of the 1960s.

A bass player with jazz leanings, who had studied at Berklee College of Music, Marker was a member of the legendary Rising Sons between 1964 and 1966, along with Ry Cooder and Taj Mahal.

During this time he hung out with Don Vliet in Los Angeles. He helped with Vliet's musical education and played with the Magic Band on a number of occasions, but was unwilling to kow tow to the large Beefheart ego on a regular basis.

Marker was involved in the early production work on Safe As Milk. He stood in for Jerry Handley on bass at live shows during 1964-67 and joined the Magic Band for a short spell in 1968-69, including playing on a couple of tracks on Trout Mask Replica.

Two other bands of his, the Jazz Folk and the New World Jazz Company (which also included John Locke, Randy California and Ed Cassidy before they formed Spirit) were never recorded. His band Fusion recorded a 1969 album Border Town which featured Ry Cooder.

In 1978, he featured on an album by Juicy Groove, alongside vocalist Michael Rainbow Neal (ex-Seeds), guitarists Mars Bonfire (ex-Steppenwolf), Elliot Ingber (ex-Mothers of Invention and Magic Band) and drummer "Thundercloud", son of former bandmate Ed Cassidy.

He has played in numerous bands (and with many legendary performers) and been a regular session musician over the years, as well working as an engineer/producer. He is now retired from the music business but still maintains an active interest (especially in Beefheart-related matters).