'The Defiant Ones'

Allegedly, director Stanley Kramer wanted Sidney Poitier and Marlon Brando to star in the film.

Other rumors had Elvis Presley interested in playing Joke alongside Sammy Davis Jr. as Noah.

At some point, the role of Joker was offered to veteran actor Robert Mitchum, who would've been great in the role (better than Tony Curtis, for sure).

Mitchum declined. At the age of 14, he actually was sentenced to and escaped from the chain gang in Georgia. He noted that a white prisoner would've never been bound with a black prisoner. The premise, he stated, was too unbelievable.

In 1953, Mitchum starred in White Witch Doctor, in which he played a hunter in the African wild, who agrees to escort a nurse through the wilds of the African jungle, escaping gorillas, hostile natives, lions and all the other realistic shit that happens.

The anecdote about not being chained together with Sidney Poitier is considered false even though Mitchum put it his book.

It's worth noting that Mitchum also had some unfortunate comments about the Jews in the 1980s. He was also an alcoholic and was one of the first celebrities to get busted for weed back in the late-1940s.

Either he was a badass or total dick, hard to tell.