The MSE series, which is also referred to as the MSE-series Maintenance Droid, represented a line of maintenance droids. A specific model within the MSE series of droids was the MSE-6 series maintenance droid.
The initial appearance of an MSE series droid occurred in the form of an MSE-6 series maintenance droid in the original Star Wars film Star Wars: Episode IV A New Hope. Production designers conducted tests on the droid on March 15, 1976, at which time it received the nickname "baby box." Gilbert Taylor, a cameraman, filmed the droid's test run, which was directed by George Lucas. For the 2005 film Star Wars: Episode III Revenge of the Sith from the prequel trilogy, on November 18, 2004, Lucas requested that Industrial Light & Magic render a mouse droid model, similar to the one featured in A New Hope, with the goal of utilizing the fleeing droid to depict "rats leaving a sinking ship." Lucas, at that point, called the mouse droid a "box droid."