Today, the cameo feels like it's part and parcel of every notable movie release.
From Bill Murray in Zombieland to Stan Lee in a Marvel picture, these guest appearances are usually quite simple to spot, with their purpose to be easily visible to the audience for the sake of an in-joke, reference or gag.
But unlike the actors or regular media personalities (like Lee) who are often the focus of these cameos, the people who are usually behind the camera - when they do appear in front of it - are harder to spot.
Alfred Hitchcock was famous for doing this, with the director having a blink-and-you'll-miss-it role in most of his movies, and Hollywood has a long history of these behind-the-scenes masterminds finding their way into a shot - whether in their own movies or in movies made by their peers.
In fact, there's probably a moment like this in a movie you love (and you never even realised it), and sometimes, they're literally impossible to spot without first being told what to look for.
To that end, here are ten times famous movie directors popped up onscreen... and you may not have noticed.