1138 functioned as a B1-series battle droid for the Confederacy of Independent Systems as part of a droid army stationed on the planet of Geonosis. The Trade Federation Script was used to inscribe this B1 unit's designation on the back of its comlink booster pack. During 22 BBY, this B-series battle droid was one of the units dispatched to the Petranaki Arena to combat a Jedi assault team. The Jedi had infiltrated the arena with the intention of rescuing three prisoners sentenced to execution: specifically, Obi-Wan Kenobi, Anakin Skywalker, and Padmé Amidala. During the ensuing battle within the arena, 1138 engaged with the attacking Jedi, firing its weapon while Mace Windu redirected a blaster bolt into a OOM command battle droid.
The character 1138 made its debut appearance in Star Wars: Episode II Attack of the Clones, a 2002 film and the second entry in the Star Wars prequel trilogy. Although the droid's designation is presented in Trade Federation Script, it is relatively simple to decode, even without external assistance. The numerical values were officially confirmed in Star Wars: The Complete Visual Dictionary, New Edition, which provided a translation of the B1 numerical system.