"John Hartman" is an United States/American drummer who was a co-founder and original drummer of the Doobie Brothers. At the band (music)/band's inception, Hartman was the sole drummer. However, in late 1971, the group added second drummer Michael Hossack, and the dual-drummers formation has persisted ever since. (Hossack was replaced in 1973 by Keith Knudsen.)
Hartman played on all of the Doobie Brothers' major chart-topper/hits of the 1970s with both Tom Johnston (US musician)/Tom Johnston and Michael McDonald (singer)/Michael McDonald. He left early in 1979 following a promotional tour in support of the award-winning Minute by Minute album to look after Arabian horses on his California ranch.More John Hartman on Wikipedia.