Robin Williams was reportedly lined up to play Harvey Milk in Gus Van Sant's biopic before Sean Penn ultimately took the role and won his second Best Actor Oscar for the 2008 film. Director Van Sant revealed he had held meetings with Oliver Stone and Williams about the project after taking over from Stone, who had spent years developing a Milk biopic of his own. The revelation offers a glimpse into an alternate path for one of Hollywood's most versatile stars, who moved fluidly between comedy and serious drama throughout his career.

Van Sant, who had previously directed Williams to an Academy Award in Good Will Hunting, said the plan came together casually after a chance meeting with one of Stone's former producers in Los Angeles. Williams had already shown he could sensitively portray a gay character in The Birdcage, but by the time Milk went into production he was arguably too old to convincingly play the union organiser and politician during the relevant period of his life. Penn, ten years younger than Williams, took the role instead and used makeup to age convincingly, delivering a subdued performance widely praised for its accuracy to archive footage of the real Harvey Milk.