The villain who steals the shrink ray in the first Despicable Me is Vector. His real name is Victor Perkins, and he is Gru’s principal rival in the film. Vector is the son of Mr. Perkins, president of the Bank of Evil, which previously refused to finance Gru’s plan to steal the Moon.
Vector first establishes his reputation by stealing the Great Pyramid of Giza and replacing it with an inflatable replica. He then obtains the shrink ray during a confrontation involving Gru. Gru needs the device for his plan to shrink and steal the Moon, but Vector’s theft turns the machine into the central object of their rivalry.
Vector later uses the shrink ray as part of his own attempt to reach the Moon. Gru adopts Margo, Edith, and Agnes partly to get close enough to recover it, though caring for the girls eventually changes his priorities. The shrink ray is temporary: objects gradually return to normal size. Vector’s plan ultimately fails, leaving him stranded on the Moon. Mr. Perkins is Vector’s father, not the thief.