Kaufmann's career was almost entirely bound up with Fassbinder and petered out after the director's death. He is actually a much more interesting figure for his role in Fassbinder's life than for any of the competently played but often minor roles he essayed in the filmmaker's oeuvre. Married and the father of two when he became involved with Fassbinder, Kaufmann was that rare figure who was not perennially kept off balance by the tortured genius' immense ego and seething temperament. Indeed, it was Kaufmann who did the upsetting. During their affair in 1970, Kaufmann could accede to Fassbinder's wishes or drive the director mad with jealousy by spending time with his wife or other male sex partners. Fassbinder, meanwhile, kept purchasing Lamborghini cars for the object of his desire which Kaufmann continued wrecking; once the two did the honors together on a Mercedes. Kaufmann's one major lead for Fassbinder, in the title role of the bizarre revisionist Western, "Whity" (1970) was an excuse for location shooting in which Fassbinder hoped to have Kaufmann all to himself.
Perhaps to minimize Kaufmann's inexperience, Fassbinder cast him in undemanding roles named 'Gunther' in several films; he also used the actor as a projection of his own fantasies, playing up Kaufmann's working-class swarthiness as a farmer in "Die Niklashauser Fahrt" (1970) or as a chauffeur in "In a Year of 13 Moons" (1979). "Whity" was the most extreme example of this tendency, with Kaufmann as a mistreated laborer who rebels and kills his exploiters. After their affair ended, Kaufmann acted in his first non-Fassbinder effort, Hans-Jurgen Syberberg's odd and compelling "Ludwig-- Requiem for a Virgin King" (1972).
Kaufmann did not return to film until later in the decade when, as with much of Fassbinder's company, he fell back in favor with the director, this time as a friend. Once more, he played small iconic roles as a GI in "Veronika Voss" (1982) and an American in "The Marriage of Maria Braun" (1978). Two of his last efforts alongside Fassbinder aptly showed art--and the director's fantasies--deliberately imitating life. In a sensuous adaptation of Jean Genet's "Querelle" (1982), Fassbinder's last directed film, Kaufmann was Nono, the barman who gets to rape male customers who lose at dice while playing to have sex with the bar's female owner. And in the police drama "Kamikaze '89" (1982), directed by Wolf Gremm, Fassbinder played an inspector dealing with a bomb threat in a building, with Kaufmann cast as his loyal sidekick. Kaufmann later played roles in the political anthology "War and Peace" (1982) and the hit farce "Otto--Der Film" (1985). He also recorded songs composed by Peer Raben, who had scored most of Fassbinder's films.