Grim and his host, Alex. And no, it's not that Alex is particularly short... it's more that Grim is unnaturally tall and large.

If I had bothered to color it, you'd be able to tell more easily that their fur pattern and colors are the exact some.

I am in love with Alex's expression here; it suits him well, seeing as how he's the unwilling host of dear old Grim. It makes perfect sense that, if he were ever to stand beside the spirit (which he can't, they're in the same body), he'd look rather unhappy.