M4-1S was a astromech droid during the Galactic War between the Galactic Republic and the reconstituted Sith Empire.
Behind the scenes
The M4-1S Astromech Droid was a gift given to all players through their mailbox in Star Wars: The Old Republic as a gift for Star Wars Day starting on May 4, 2015. It was first announced in a livestream centered on Game Update 3.2.