 He was also a stage and film set designer with commissions from La Scala, Spoleto, the Glyndebourne Festival, the New York City Opera and the Metropolitan Opera for productions like "La Gioconda," "Esclarmonde", "The Last Savage", "The Daughter of the Regiment", "L'Elisir d'Amore" (Metropolitan Opera), "Aida" and "The Magic Flute" (New York City Opera).Montresor worked with film directors Federico Fellini, Vittorio De Sica and Roberto Rossellini among others.Montresor had a longer term affair with the writer Anne Cumming in the 1950s whilst she was married and also had many other gay and straight affairs.