All of his characters inhabit two fictional universes
UPDATE: Tarantino revealed that one character in The Hateful Eight is related to someone in another of his films. We worked out who it is.
Fans have speculated for years over the hyper-violent universe that Quentin Tarantino’s characters inhabit. After all, we know that Reservoir Dog’s Vic Vega and Pulp Fiction’s Vincent Vega are brothers, and that True Romance’s Lee Donowitz is the son of Inglorious Basterd’s Donnie Donowitz. We also know that they all smoke that same fictitious brand of “Red Apple” cigarettes.
But now, Tarantino himself has finally weighed in on these theories. Speaking to The Project on Monday night, the Hateful Eight director confirmed that his special movie universe is indeed real – and that there’s not only one, but two.
“There is actually two separate universes,” he explained. “There is the realer than real universe, alright, and all the characters inhabit that one. But then there's this movie universe. So From Dusk Till Dawn, Kill Bill, they all take place in this special movie universe. So when all the characters of Reservoir Dogs or Pulp Fiction, when they go to the movies, Kill Bill is what they go to see. From Dusk Till Dawn is what they see.”
Take Pulp Fiction’s Mia Wallace, when she was describing her pilot episode of Fox Force Five. The description she gives to Vincent Vega is basically exactly the same as Kill Bill – which means that this pilot she filmed probably went on to be a film, and that Mia secured the leading role. Make sense?

Tarantino has also implied that a character in his newly-released Hateful Eight has got a secret family member lurking in that “realer than real” universe. “I don’t want to say it point blank ‘boom!”, but if you’re a fan of my work and are familiar with it you could be a bit of a detective,” he told Digital Spy. “I will say that there is one character amongst the eight that is related to one of my other characters in one of my other films.”
“I can’t explain the relation because that would tip my hat a little bit too much,” he hinted. “The only other clue I can give… is that the actor was originally cast as that character in the other film but they weren’t able to do it due to a scheduling conflict.”
(H/T Pedestrian)