The Star Wars version of the T-800, the IG-88 showed up for a whole two seconds in Empire Strikes Back, but quickly became a fan favorite. Why wouldn't he? The dude has a ridiculous head that looks like a soda can, but he's still somehow one of the most fearsome bounty hunters in the galaxy.
During the '90s explosion of Star Wars expanded universe content, IG-88 got a kickass backstory: there were five IG-88 assassin droids created for the express purpose of murder, but the robots had other plans. They all decided that, as cool as the universe was, droids deserved to rule. A revolution needed to happen.
To start, they captured the droid factory Mechis III, copying their maniacal, homicidal thoughts into droids sent all over the universe. Even otherwise peaceful robots like R2 units were implanted with revolutionary zeal and programmed so that when the time came, they'd rise up and murder their masters. Of course, they needed a cover so people wouldn't wonder what was happening on Mechis III, so they decided to moonlight as bounty hunters while the revolution got going.
That's not even the most insane part of the story. Eventually four of the droids were blown up in various adventures, and the last one decided to go big or go home. He found the Death Star II computer core and uploaded his consciousness into it, becoming the battlestation. With that immense power, he didn't do something like try to blow up random planets; instead, he did what any of us would have done: screwed with the Emperor by slamming doors in his face.
IG-88 ended up running the computerized defenses of the Death Star at the Battle of Endor—not only were the Rebels fighting the Empire, they were also fighting IG-88. When Wedge and Lando blew up the Death Star, they actually killed two birds with one stone: ending the Empire and the IG-88 Droid Revolution. Not bad for a day's work.