Transformer

The Transformer is a device used by the Simpsons in order to aid them in their shapeshifting abilities. Each Simpson is gifted a Transformer when they reach a certain age, along with a mandatory training class in its ability. Bart stole his Transformer and left Planet Simpson, bringing it to the Land of Ooo where it was stolen and used by some of its inhabitants, most notably members of TFAWPS and S.E.C.R.E.T. Eventually, Bart received his Transformer back.