Peter Kastner (1 October 1943 – 18 September 2008) was a Canadian actor who achieved prominence as a young man in lead roles in the popular 1964 film Nobody Waved Good-bye and in Francis Ford Coppola's 1966 well-received comedy You're a Big Boy Now.

[4] His breakthrough role was in the title role in Francis Ford Coppola's 1966 comedy You're a Big Boy Now, which starred Elizabeth Hartman, Geraldine Page, Rip Torn, Karen Black, and Julie Harris, in which Kastner played an earnest young man who moves from his parents' house to New York City and struggles with confusing relationships.

[5] Kastner starred in the 1968–1969 ABC sitcom The Ugliest Girl in Town, where he played Timothy Blair, a man who dressed in drag as a favour to his photographer brother.

[1] He starred in the 1977 CBC Television sitcom Custard Pie as Leo Strauss, the manager of a musical group of that name,[9] but the series was not popular or critically well received.

[citation needed] Starting in the early-to-middle 1970s, Kastner became increasingly emotionally troubled and eventually became bitterly estranged from his family, making especially negative allegations about his mother.

[11][3] On the occasion of a showing of Nobody Waved Good-bye for a Toronto International Film Festival sesquicentennial celebration of Canadian cinema in 2017, Kastner's siblings wrote an article commenting about his early promise and the later difficulties in his life.