In the mid-'70s, a young sound designer named Ben Burtt gave these sounds a name: "the Wilhelm scream," after a character in one of the earliest films that utilized the sounds. A couple of years later, Burtt was hired to work on a film called Star Wars. As an homage, he overdubbed the scream onto a scene in that film. Then he overdubbed it onto a scene in The Empire Strikes Back. And Return of the Jedi. A fellow Lucasfilm sound designer began using the Wilhelm too, in Raiders of the Lost Ark and Indiana Jones and the Temple of Doom, among other movies. And thus a film-geek in-joke was born. In the last 30 years the Wilhelm has been used winkingly in dozens of movies and TV shows, from Reservoir Dogs and The X-Files to Aladdin and Return of the King. More details are at Hollywood Lost and Found.