It’s important to note that the idea of a shared universe can just act as a very small part of a film. It may be just a winking cameo, like when Dr. Raymond Stantz (Dan Aykroyd) from Ghostbusters, drops in for a quick scene in Casper.
Other times, the concept of a same universe theory is the groundwork for an entire network of movies. You've likely heard of the Marvel Cinematic Universe, combining the forces of many different superheroes. But there are also a few post-modern directors that elicit rabid same universe fan theory. The same universe theory allows us to loosely link all of Quentin Tarantino’s movies, his canon of work is called Tarantino Universe. Sometimes his characters are related, sometimes they work together, heck sometimes they just go to the movies together. Some of the Tarantino connections are stronger than others, the ones listed below are totally cut and dry.
Casper and Ghostbusters
This shared universe makes a lot of sense since both films obviously center around the whole ghost thing. The 1984 comedy classic features three parapsychology professors who set up shop as ghost removal professionals. In 1995's Casper, an abandoned house is littered with three not so nice ghosts and their nephew Casper, "the friendly ghost." The house's owner calls upon an expert in ghost removal and who shows up?
Dr. Raymond Stantz (Dan Aykroyd) dressed in complete ghostbuster's apparel enters the picture for a brief wink-wink cameo. However, he doesn't have his full crew. Casper's three menacing uncles prove to be too much for Ray. After his ghost defeat, he races out of the house and informs the owner, "Who you gonna call? Someone else."
Kevin Smith's View Askewniverse
Independent film director extraordinaire Kevin Smith is from the Garden State of New Jersey. Most of his films exist in the same universe, called the View Askewniverse, which is named after Smith's production company, View Askew.
Films in this universe include Clerks, Mallrats, Chasing Amy, Dogma, Jay and Silent Bob Strike Back, and Clerks 2. Those movies all take place in the New Jersey and New York area and share several of the same characters and themes. The View Askewniverse also consists of comics, an animated TV series, and several of Smith's short films. Jay and Silent Bob appear in all of the films in the View Askewniverse.
Pulp Fiction and Reservoir Dogs
We know for sure that Vincent Vega from Pulp Fiction and the sadistic Vic Vega (aka Mr. Blonde) from Reservoir Dogs are brothers. In fact, director Quentin Tarantino even talked about his plans for both a sequel and prequel to his first two feature length films that would star John Travolta and Michael Madsen. Tarantino explained his idea on the Opie and Anthony radio show, "I even had a title for it. It was called Double V Vega. It would have taken place during the time Vincent Vega was in Amsterdam, when he was running one of Marcellus' clubs in Amsterdam. And Vic goes to visit him."
Who wouldn't love to see the hitmen Vega brothers together on the silver screen possibly discussing the merits of a Royale with Cheese? However, Tarantino admitted the time to make those movies has passed. "But we’re a little older now, and since they both died – it would have to be a prequel,” said Tarantino. “I actually came up with a way I could have done it, even being older and dead where they all had older brothers and both of their brothers got together because the two guys died. And they wanted revenge or something like that. But now, [the actors] are too old for that.”
Marvel Cinematic Universe
The rights to all of the Marvel Comics (save for six characters) to Marvel Films. The company has been extremely successful in bridging together characters and stories in order to create the Marvel Cinematic Universe. Comic book movies are more successful than ever before, and there is certainly no shortage of crossovers and mega franchises, which are consistently raking in monster numbers at the box office.
It all started with Iron Man in 2008. Since that time Marvel has produced several films within the same universe, including: Captain America: The First Avenger, The Incredible Hulk, The Avengers, Thor, Guardians of the Galaxy, and Ant-Man. Of course, all of those movies are part of their own franchises and have spawned several sequels as well.