Clay

A fat little space alien made out of clay.

He got on a broken spaceship to take it for a joyride and ended up stuck on Earth. 

Stuck is a strong word, he likes Earth better than his home planet, he's particularly fond of strawberry flavoured dairy drinks.

He's roughly the size of a large house cat, but he can be a bit bigger or smaller depending on the day. He is made of clay after all. (About 20 inches from feet to ears)