Revenge of the Sith - 2-1B Surgical Droid. Palpatine takes the gravely wounded Darth Vader to Coruscant. A team of surgical droids, including a 2-1B series droid, uses diagnostic and surgical equipment to treat Vader's injuries, attach mechanical limbs, and encase him in the black armored suit that he'll wear the rest of his life.
Empire Strikes Back - 4-LOM. A programming glitch changes 4-LOM from a protocol droid to a thief and a tracker of fugitives. Jabba the Hutt teams him with the bounty hunter Zuckuss, creating a formidable duo that successfully combines intuitive mysticism with emotionless logic.