Smith told EW that he turned down the part because his character would’ve been supporting the white bounty hunter character, Dr. Schultz, played by Christoph Waltz.
“Django wasn’t the lead,” Smith told EW. “So it was like, I need to be the lead. The other character was the lead!”
Ironically, according to the credits, Waltz was considered the supporting actor for which he won an Oscar while Jamie Foxx, who played Django Freeman was promoted as the movie’s lead, even though according to Smith, he was not.
Read more at Entertainment Weekly.