Arex was a Jedi training droid who spent many years with Jedi on the river moon of Al'doleem, a moon in the galaxy's Mid Rim. During the early stages of the Jedi Purge, Arex was present on the moon with Jedi Master Kirak Infil'a and was tasked by Infil'a with preparing the mountains defenses when something dark was approaching. When Infil'a confirms it is a sith, the droid runs to intercept him, but before it can, Vader takes its weapon, and throws the droid off the mountain. Later, when Vader his thrown off the mountain by Infil'a, he lands near the droid, who has survived. Arex then tells Vader that he is defeated, but Vader in response to this, crushes the droid, destroying it, and uses its parts to repair himself.

Note: His voice must be synthetic