MR-T3 was an R4 astromech droid produced by Industrial Automaton. This droid served the Galactic Republic during the Clone Wars. In 19 BBY, MR-T3 found itself at the Republic Center for Military Operations, situated on the galactic capital planet Coruscant, alongside the protocol droid known as R-A7. As the two droids ambled along a hallway within the base, Jedi Padawan Ahsoka Tano—who was trying to escape the facility after being wrongly accused of the murder of a prisoner there—came running down the hall towards them. Tano vaulted over MR-T3, causing the astromech to spin around while emitting a series of binary beeps; simultaneously, R-A7 shook its fist at the Jedi in anger. MR-T3 featured plating with black and white coloring, and a black sensor was integrated into its conical frustum-shaped dome.
The initial appearance of MR-T3, though without identification at the time, occurred in "The Jedi Who Knew Too Much," which was the eighteenth episode of the animated television show Star Wars: The Clone Wars' fifth season. This episode was broadcast on February 16, 2013. Later, the droid received its identification through concept art by JP Balmet, revealed as part of the Episode Guide that accompanied the show on StarWars.com; this guide also mentioned that MR-T3 was essentially a retextured version of the astromech droid M5-BZ, who had made an appearance earlier in the same season.