Marvin (Hitchhiker's Guide to the Galaxy)

Good things come in small packages, and Marvin is definitely one of a minute stature. However, as small as he is, he does have quite one of the largest brains this galaxy, or any other, has ever known. Sure that might give him the tendency to over-think things and stress out about them, but that still gives him an amazing head on his shoulders... a very LARGE amazing head.