The film takes place in 1967, as then Heavy Weight Champion of the World Muhammad Ali refused to enlist and go fight for the USA in Vietnam; his objections to the war were very public, and he was convicted and sentenced to serve time in prison, during which he appealed his case, which would go all the way to the Supreme Court.
This was all around the time the public began turning against the war, and thus support for Ali grew; eventually, some years later, the Supreme Court would reverse his conviction.
The film stars Christopher Plummer, Frank Langella, Danny Glover, Ed Begley Jr., Barry Levinson, Bob Balaban, and Kathleen Chalfant.
Danny Glover will play Supreme Court Justice Thurgood Marshall; Begley, Levinson, Balaban and Chalfant will play Justice Harry Blackmun, Justice Potter Stewart, an advocate for Vietnam veterans, and Justice Marshall Harlan's wife respectively.
Christopher Plummer is playing Harlan, while Frank Langella is Chief Justice Warren Burger.
As for who's playing Ali in the film, director Frears opted not to cast an actor to play Muhammad Ali, and is instead using archival footage of Ali in the film, which focuses more on the Supreme Court judges and their decision-making.
The film screened at Cannes last week, and will be making its debut on HBO sometime this year.
THR was present for the Cannes screening, and called it, in a review, "an engaging, overly snappy look at little-known aspects of a fascinating Supreme Court case."
They also got to chat with Frears about the making of the film, and that video interview follows below, in which you'll find select scenes from the film: