Cinnamon Carter was a fashion model/actress and a member of the IMF; she actually served as de facto mission team "captain" in one episode, "The 'Action!' Mission." Her primary role, in her own words, was to "do what comes naturally." She acted as various characters required by the jobs, often distracting male enemies with her sultry looks and seductive manner. She was skilled in unarmed combat, capable of disabling men larger than her. In the world of grand-scale confidence games, which method the IMF used most commonly, Carter was a "roper," whose duties involved directing the mission target into the "big-store" setting in which the team would deal against and undo him or her.
Carter was acted out by Barbara Bain, who left after Season 3 with her husband Martin Landau (who played Rollin Hand). The couple continued acting together, most notably in the British sci-fi TV series Space: 1999. However, they subsequently divorced.
(The reasons for Carter's and Rollin Hand's departures from the IMF were not revealed; however, they might have been dismissed because of being married agents.)
As far as the character of Cinnamon Carter, it is unknown whether she retired or moved on to some other work, however in the 1990s Bain reprised the role for an episode of Diagnosis Murder, at whose end she was re-activated.