What student short did George Lucas expand into THX 1138?

The student short George Lucas expanded into THX 1138 was Electronic Labyrinth: THX 1138 4EB.

Lucas wrote and directed the 15-minute black-and-white science-fiction film in 1967 while studying at the University of Southern California. It depicts a tightly controlled technological society in which THX 1138 attempts to escape constant surveillance and conditioning.

The short became the foundation for Lucas’s first feature film. In 1971, he reworked its premise and final escape into THX 1138, produced by Francis Ford Coppola’s American Zoetrope. The feature expanded the short’s dystopian world and starred Robert Duvall as THX 1138 and Donald Pleasence as SEN 5241.

A common mix-up is to treat THX 1138 as the original student title. THX 1138 is the later feature; Electronic Labyrinth: THX 1138 4EB is the earlier USC film. The short was later included with home-video releases and entered the National Film Registry in 2010.