He is known for his roles as the witty Det. Ron Harris in the television sitcom `` Barney Miller '' ( 1975 -- 82 ) , and as the spiritual Shepherd Derrial Book in the short-lived 2002 science fiction series `` Firefly '' and its sequel film `` Serenity '' .
He is best known for his roles as Det. Ron Harris in the television sitcom `` Barney Miller '' ( 1975 -- 82 ) and as Shepherd Derrial Book in the short-lived 2002 science fiction series `` Firefly '' and its sequel movie `` Serenity '' .