Jamie Foxx, 45, was eventually cast in the role of Django -- a freed American slave who assists Christoph Waltz's Dr. King Schultz, a German dentist/bounty hunter, with capturing and killing his enemies in exchange for helping Django reunite with his wife, Broomhilda, played by Kerry Washington.
Jackson, 64, ultimately signed on for the scene-stealing role of slave supervisor Stephen, the right-hand man of Calvin Candie, a wealthy plantation owner portrayed by Leonardo DiCaprio.
"I'm the power behind the throne. I'm like the Spook Cheney of Candyland," Jackson told reporters at a New York press conference before the movie's late 2012 theatrical release.
"Yeah, I'm all up in that. To tell this story, you have to have that character, specifically in that type of setting," Jackson explained. "I got the script from Quentin. He called me and told me he wrote a western and he wanted me to read Stephen, and I complained about being 15 years too old to play Django. When I read the script, I called him back and said, 'So, you want me to be the most despicable Negro in cinematic history?' We both kind of laughed together and said: 'Yeah! Let's get on that.'
"Not only was that a great artistic opportunity to create something that was iconic and to take what people know as Uncle Tom and turn it on its head in a powerful way; it also gave me the opportunity to do some really nasty [expletive] to the person who got the role I should have had," Jackson said.
"Django Unchained" was a Best Picture Oscar nominee this year, but lost out to "Argo."
Waltz and Tarantino won Oscars for Best Supporting Actor and Best Original Screenplay respectively for the film, which has been the top-selling DVD and No. 1 rental in the United States for the past two weeks.
Jackson and Tarantino previously collaborated on the films "True Romance," "Pulp Fiction" and "Jackie Brown."