In every star wars movie, there is this distinct yell. It is generally used once.
What is the origin of this scream? Was it popularised by George Lucas?
There's no point in not answering this- as your youtube link indicated, it's the Wilhelm Scream, and originated a fair bit earlier than Lucas' work:
The Wilhelm scream originates from a series of sound effects recorded for the 1951 movie Distant Drums. In a scene from the film, soldiers are wading through a swamp in the Everglades, and one of them is bitten and dragged underwater by an alligator. The scream for that scene was recorded later in a single take, along with five other short pained screams, which were slated as "man getting bit by an alligator, and he screamed." The fifth scream was used for the soldier in the alligator scene—but the 4th, 5th, and 6th screams recorded in the session were also used earlier in the film—when three Indians are shot during a raid on a fort. Although takes 4, 5, and 6 are the most recognizable, all of the screams are referred to as "Wilhelm", by those in the sound community.
Now, as far as Lucas' use:
The Wilhelm scream's revival came from motion picture sound designer Ben Burtt, who discovered the original recording (which he found as a studio reel labeled "Man being eaten by alligator") and incorporated it into a scene in Star Wars. Burtt is credited with naming the scream after Private Wilhelm (see The Charge at Feather River). Over the next decade, Burtt began incorporating the effect in other films he worked on, including most projects involving George Lucas or Steven Spielberg. (It is used in all of the Star Wars and Indiana Jones movies.)
This specific effect was even used in The Hobbit. From same Wikipedia article:
The Wilhelm scream has become a cinematic sound cliche, and by 2011 had been used in many instances, including over 225 movies, television shows and video games (and video game advertisements). Some directors, most notably George Lucas (Star Wars original trilogy and prequel trilogy movies), Quentin Tarantino, and Peter Jackson (in two of the Lord of the Rings movies and also The Hobbit) include it in almost every one of their productions.