The Adventure Path says that he's a human, but looking at his portrait and reading his name, it seems pretty obvious to me that he's a gnome. Either an elderly one or a bleachling.
My co-GM (I'm running this with Hexcaliber,) was skeptical at first, thinking it might make players not take him seriously... but he trusted my instincts, and suddenly, Father Grimburrow's one of the most resonant characters in Ravengro for my players. He's also a character my co-GM decided he had to claim for himself. He does a great job with him, too, but then Hex is great at this kind of role.
There's just something about this grim little gnome with a stern and looming presence who doesn't take anyone's crap and doesn't hold with any adventurer fiddle-faddle that no-one can stay neutral about. Not that they like him ICly, (in fact, at least one of the characters really wishes very hard that the Father is secretly behind everything so she can kill him.) But he's super-memorable.
I'm just wondering if anyone else, like me looked at his portrait and his name and thought, "He's totally a gnome. The most awesomely grim, stern, no-nonsense gnome ever."
If so, how'd that work out for you?