Conversation so far:
What did the musician Michael McDonald do with the Doobie Brothers?
Michael McDonald sang the lead vocals on some of the Doobie Brothers' best-known songs such as Real Love, Takin' It to the Streets, and What a Fool Believes.
How long did the musician Michael McDonald sing with the Doobie Brothers?
Michael McDonald is known for his distinctive, soulful voice and as a member of The Doobie Brothers from 1975 to 1982, 1987, 2019 to the present.

Question: What instrument did he play in the band?
Self-contained rewrite: What instrument did the musician Michael McDonald play in the band The Doobie Brothers?