MZ-12 began its service to the Sith Empire during the Great Galactic War as a simple maintenance droid aboard the personal cruiser of Darth Immern. When the Darth disposed of his crew in a fit of frustration, he had to turn to the MZ unit to help manage the ship's many systems. Though not designed for such duties, Twelve was able to help guide the ship to an Imperial way station, where Darth Immern had the astromech's programming upgraded so that it could serve as his personal navigation droid.
Since Immern's death during the First Battle of Bothawui, Twelve has been in search of a new home. It is now quite adept with ship comms and sensors, and is known to have a bit of an ego about it.