1825, "company, band," from Fr. troupe, from M.Fr. troupe "company" (see troop). Trouper is "actor or performer in a theatrical troupe;" transf. sense of "reliable, uncomplaining person" is attested from 1959 (but the first recorded reference describes the usage as "old-fashioned").
1545, "body of soldiers," from M.Fr. troupe, from O.Fr. trope "band of people, company, troop" (13c.), probably from Frank. *throp "assembly, gathering of people" (cf. O.E. šorp, O.N. thorp "village," see thorp). OED derives the O.Fr. word from L. troppus "flock," which is of unknown origin but may be from the Gmc. source. The verb is attested from 1565, "to assemble;" meaning "to march" is recorded from 1592; that of "to go in great numbers, to flock" is from 1610. Trooper "soldier in the cavalry" is first attested 1640; extended to "mounted policeman" (1858, in Australian) then to "state policeman" (U.S.) by 1911.