R3 was built during the clone wars as part of a line of astromechs destined to serve on the front lines of the war, but wasn't activated until the empire had already taken over. He was assigned to the Imperial military and worked for some time on a Star Destroyer as a navigation and repair droid. His assigned maintenance technician, however, was neglectful of his duties and never wiped the little droid's memory. As a result, R3 was free to develop a highly unusual and erratic personality, owing to the extreme conditions for droid workers aboard the destroyer. This personality drove him to escape the Imperial Navy, and after spending some time in the outer rim honing his craft he joined the Rebellion.

Cause: Non-human rights.

R3 hates nothing more than the fact that he and others like him are not treated with respect, instead being viewed as tools and servants. He's not opposed to performing the function he was designed for and understands the fundamental differences between an organic and a droid, but he will not accept being treated worse or valued less than an organic. This personal struggle has turned R3 into a raving idealist who attempts to improve the plight of the galaxy's droids by fighting back against the Empire, who are the worst perpetrators of the abuse.

Using this section for duty because swsheets is dumb.

Duty: Tech procurement.

R3 hates the Empire, but his love for machines is an equally powerful reason for his service in the rebellion. As far as R3 is concerned, there's no better time to design, construct, and test interesting ideas than a war, and the Rebellion's emphasis on quality rather than quantity makes it the perfect environment for the technological fanatic. He is convinced that better machines is the way to bring the Empire down.

R3's transparent dome reveals a brilliant but unstable and erratic processing center. The droid is highly prone to inventing not only machines, but also conspiracy theories, insults, and nonsensical conjectures, and owing to his self-installed voice box everyone around him knows it. He is painfully aware of the place that he and other droids hold in society, and this has caused him to develop not only an obsession with droids, but also a paranoid and cranky personality. He's not incapable of forming friendships with organics, however, provided he's treated with the respect he believes he deserves.