MacGuffin's were popularized in the 1930's by thriller extraordinaire, Alfred Hitchcock, but were in use long before that. The earliest known use of a MacGuffin type story element was the Sampo, a mysterious item that brought its owner good luck, in the 19th century Finnish epic, The Kalevela. In movies, it was used in many silent films, though they were called "weenies." The term was used by silent film actress Pearl White to describe any physical object that made the hero and villains chase after each other in her many films. I have no idea why she decided to call them "weenies," but I'm glad it didn't stick. Anyway, Hitchcock came up with the term while shooting his 1935 film, The 39 Steps and ended up using the MacGuffin in most of his other movies. He later explained how he came up with the name in an interview in the late 60's:
"It might be a Scottish name, taken from a story about two men in a train. One man says 'What's that package up there in the baggage rack?', and the other answers, 'Oh, that's a McGuffin'. The first one asks 'What's a McGuffin?' 'Well', the other man says, 'It's an apparatus for trapping lions in the Scottish Highlands'. The first man says, 'But there are no lions in the Scottish Highlands', and the other one answers, 'Well, then that's no McGuffin!' So you see, a McGuffin is nothing at all."
Hitchcock had a very interesting view on MacGuffin's however, as he felt that they weren't important things in the story, and shouldn't be cared about by the audience. Directors like George Lucas have disagreed with this mindset and claim that the MacGuffin should be cared about just as much as the dueling heroes and villains. Some directors loathe using the MacGuffin at all, the most prevalent probably being Steven Spielberg. Spielberg, in response to the mixed reviews to Indiana Jones and the Crystal Skull commented that he felt it was because people didn't like the MacGuffin in the film (the crystal skull) and that he never really liked using the MacGuffin.
It's hard not to see a movie that doesn't have some sort of MacGuffin, but here are a few that stand out. Probably the most famous is the meaning of "Rosebud" in Citizen Kane. The whole movie revolves around this reporter trying to find out what Charles Foster Kane meant with his dying word of "Rosebud." Turns out it was the name of his sled. If you didn't know that spoiler than you've been living under a rock, because I'm pretty sure that was the second movie spoiler I had ever learned about as a kid, right behind Darth Vader being Luke's father. Another popular example of a MacGuffin in film is the titular Maltese Falcon. Probably one of my favorite noir films of all time, it shows how an object of no real relevance can cause a whole lot of problems. Another MacGuffin that people talk a lot about is the mysterious briefcase in Pulp Fiction. Nobody knows what's inside of it, but in the end it doesn't matter. All we need to know is that whatever is inside is something that is worth killing someone over. Tarantino made it clear that the audience doesn't need to know what the MacGuffin is to make the plot work, they just need to know that there is a MacGuffin.
Other notable MacGuffin's include the rabbit's foot in Mission Impossible III, the Genesis device in the Star Trek movies, the holy grail in Monty Python and the Holy Grail, Indiana Jones and the Last Crusade, and The DaVinci Code (apparently that's a popular one), the death star plans in Star Wars, the ark of the covenant in Raiders, the ring in Lord of the Rings, and unobtanium in Avatar. There are countless ones, and they aren't just used in movies. In TV there is, just to name a few, the intersect from Chuck, the Rambaldi device in Alias, and my personal favorite, the orb from The Adventures of Brisco County Jr. You may hate MacGuffin's or you may love them, but they will continue to be used as long as there are needlessly complicated stories to tell.