In our current era of endlessly self-referential IP-driven entertainment, the cameo is king. In big blockbuster movies, they provide an outlet for actors who just can’t swing the time commitment of a six-movie deal to appear as beloved characters for a scene or two before disappearing forever or getting killed off. The world of superheroes is full of such cameos—just watch any Deadpool or Thor movie and you’ll get the gist.

In others, the cameo serves a variety of purposes. Celebrities often play themselves to give movies a certain real-world edge. Actors will sometimes use cameos to play against type, appearing as a character they otherwise would never consider. Characters from certain movies or franchises can appear in other movies, connecting them together in a shared universe. Cameos are often used to stunt-cast actors who wouldn’t have been able to do the whole movie, instead popping up for a scene, absorbing the applause from the audience, and then bowing out to let the movie continue.

The best types of cameos happen totally unexpectedly, where an actor is cast for a role seemingly at random, to the audience’s astonishment, having their bizarre yet hilarious moment and then disappearing again. Sometimes these cameos are noticeable, like Matt Damon’s ultra-dramatic Loki in Thor: Ragnarok, and sometimes you really have to squint, if you notice them at all. Maybe the best cameos are the cameos you never notice until the director reveals a bit of trivia, or someone spots an A-list actor under a mask a year later. These are the types of cameos that are invisible unless you’re in the know.

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