The first one that comes to my mind is Charles Addams, the godfather of goth! Next, but a real challenger for the lead in my book is Gahan Wilson.
Our paper started a strip called "Lido" which is about a little boy with monstrusly gothic tastes. Can't think of the artist's name, but he was obviously influenced by Wilson.
I'd also put Jack Davis in this category. Even at his most horrific, his drawings were imbued with humor. Ditto "Ghastly" Graham Ingles.
Frank Deitz's monster characatures are classic.

Can you think of others that you'd put in the list?