As a multi-instrumentalist, Marcus is highly proficient as a keyboardist, clarinetist/bass clarinetist and, primarily, as a world-renowned electric bassist, topping critics' and readers' polls for three decades.
His résumé as an A-list player brims with over 500 recording credits as a sideman on albums across the spectrum of musical styles: rock (Donald Fagen and Eric Clapton), Jazz (George Benson, Dizzy Gillespie, Joe Sample, Wayne Shorter and Grover Washington, Jr.), pop (Roberta Flack, Paul Simon and Mariah Carey), R&B (Aretha Franklin and Chaka Khan), hip hop (Jay-Z and Snoop Dogg), blues (Z.Z. Hill), new wave (Billy Idol), smooth jazz (Al Jarreau and Dave Koz) and opera (collaborations with tenor Kenn Hicks and soprano Kathleen Battle).