One of his most respected movies (and a commercial dud, which affected him deeply) is "Monsieur Klein". Which tackled the sensitive subject of Vichy France deportations of jews in 1942; and doing that in 1976 was ballsy, as it took 20 more years (1995) for France to officially acknowldge its responsability.
Mr Klein, played by Delon, is a deeply amoral individual trafficking art from hard-pressed jews fighting for their lives. Until something unexpected happens: there is another Mr Klein playing a dangerous, mysterious game with their names and identities. The movie is a nightmarish thriller where Delon character gets fascinated by the "impostor" despite the danger. That fascination and the tracking of that mysterious eponym will ultimately drive both to Drancy, then Auschwitz. Delon character and the spectator will never see the other Klein.
