And according to Samuel L. Jackson himself via NYT article,

https://www.nytimes.com/2012/12/20/movies/awardsseason/supporting-actor-category-is-thick-with-hopefuls.html?smid=nytcore-android-share

Mr. Jackson said, laughing. “I said, ‘O.K., now you want me to play the most hated Negro in cinematic history?’ And he was like, ‘Yeah!’ ”

As Stephen, Mr. Jackson must navigate a host of thorny issues about race and class, which he took in stride. “He believes in slavery, believes in the hierarchy of things, he’s the freest slave on that plantation,” he said. (In character, he added, “I have the same moral compass as Clarence Thomas does.”)