Some movies scream for more backstory, and others are fine with the characters as they've already been presented. Some tales, like Star Wars, end up muddled and confused if you introduce prequels -- especially if they introduce a host of other characters who aren't integral to the original story.
Others, like The Wizard of Oz, have long shelf lives and a rich literary background that make it easy to create new stories. That's the whole idea behind Oz the Great and Powerful.
Then there are Quentin Tarantino movies. Everyone either loves or hates him, but most cinephiles agree that he's one of the best. Not only does he have incredible visual talent, he's got one of the best ears for dialog and talent for creating characters that the idea of making a prequel to one of his movies would never cross your mind.
However, one of his best films, Jackie Brown, was actually based on a novel called Rum Punch by Elmore Leonard. Thus, we have the sticky situation of characters made indelible by Tarantino but who have backstories of their own that existed long before the director came along.
That's why there is an upcoming prequel called Switch, according to Vulture. It will star Mos Def as a younger version of Samuel L. Jackson's character, Ordell Robbie, and John Hawkes as Robert DeNiro's Louis Gara. Recently, Isla Fisher was asked to step in for the role played by Bridget Fonda in the original, though she hasn't yet made up her mind.
The only downside to this movie is that Tarantino won't actually be involved. Instead, director Daniel Schechter is attached, and this will be his first project of note for Hollywood.