C-5D1, also known as fifty one was a protocol droid who worked in the Republic prison on the planet Belsavis during the Galactic War against the Sith Empire. During the war an Imperial-backed mass breakout occurred in the prison, and one group of the Rattataki escapees known as the Blood of Talath began causing serious casualties amongst the prison guard as they appeared to pre-empt their attacks. Officer Serik, determined to discover how the Ratataki were communicating before attacks, sent C-5D1 with a Republic aligned individual into the Rattataki Battlewoods to analyse the sound there. The droid discovered that the criminals were using bird calls to communicate.
- Star Wars: The Old Republic (First appearance)