Rebo's Cat is a Saturnian Cat.
A very hungry, gray Saturnian cat, this critter was the prized pet of dictator Rebo. In 1960, to motivate Donald Duck (whom he had confused for an engineering genius) to build war machines for him, Rebo used another piece of Saturnian technology to shrink Donald to the size of a mouse, and threatened to feed him to the cat.
Behind the scenes
Rebo's Cat appears in the 1960 story Uncle Scrooge's Money Rocket. In the sequel, Rebo owns a large number of Saturnian Cats, and it is not stated whether the one original cat from Money Rocket is among them.