Conversation so far:
Was Buck Clayton a mainstream musician?
Buck Clayton was a leader of mainstream-oriented jam session recordings
When did Buck Clayton's music become mainstream?
Buck Clayton was a leader of mainstream-oriented jam session recordings in the 1950s.
Were these Buck Clayton mainstream-oriented jam sessions well received by critics?
Buck Clayton “synthesized much of the history of jazz trumpet up to his own time, with a bright brassy tone and an apparently limitless facility for melodic improvisation”

Question: What did it mean to be a mainstreamer?
Self-contained rewrite: What did it mean for Buck Clayton to be a mainstreamer?