John Cazale & Meryl Streep in The Deer Hunter, 1978
Cazale had terminal cancer during shooting and all of his scenes had to be filmed first. Because of his illness the studio initially wanted to replace him but Streep and director Michael Cimino threatened to walk if they did.
"I’ve hardly ever seen a person so devoted to someone who is falling away like John was," said Al Pacino. "To see her in the act of love for this man was overwhelming."