He's in talks for the role of Ace Woody, the sort of nasty that Tarantino specializes in.
The bounty hunter and the slave become friendly and set out to rescue the slave's wife from the vicious Calvin Candie (Leonardo DiCaprio is in that role). Woody is one of Candie's henchmen.
Tarantino wrote and is directing the film.
Costner will also be playing honest guy Jonathan Kent, Clark Kent's father, in Warner Bros. upcoming Superman movie "Man of Steel."
The Weinstein Company will release "Django Unchained" domestically. Sony Pictures will handle it internationally.
Deadline first reported the news.