Eric Clapton joined John Mayall & the Bluesbreakers after leaving the Yardbirds in order to concentrate on the blues; he was in the band from April to August 1965, and from November 1965 to July 1966.  John Mayall’s band was a revolving door of famous British musicians; but even more remarkably, bandmembers who left John Mayall & the Bluesbreakers often helped form other rock bands.  Examples include Jack Bruce, later a member of Cream with Clapton.  Shortly after Eric Clapton left for good, John Mayall & the Bluesbreakers consisted of John Mayall plus three of the founding members of Fleetwood Mac:  Peter Green, John McVie, and Mick Fleetwood.  Others include Mick Taylor, the first new musician to join the Rolling Stones since their classic line-up was formed; Jon Mark and Johnny Almond, who later formed Mark-Almond, among other musical accomplishments (not to be confused with Marc Almond of Soft Cell); top English drummer Aynsley Dunbar; and Andy Fraser, a founding member of Free. 

(May 2014)