Jolly Blackburn could be argued as the worst artist to have a best selling comic (Knights of the Dinner Table). His art is utterly horrible. It's better than what I could do, but it still is tremendously bad.
It's perfect for his comic, though. The majority of his comic involve people sitting around a table, talking about RPGs, CCGs, LARPs, and other forms of geekdom.
His comics started out in Shadis magazine as simple bits of filler. Since then, he's appeared in Dragon Magazine, launched his own comic book, and then had Knights of the Dinner Table bought out by Kenzer and Company. His "mythical" gaming system, Hackmaster, has now been made into an actual gaming system (based on the Advanced Dungeons and Dragons first and second edition rules!).
Despite how much I love his comics, their characters, and how I wait impatiently for the next issue of the comic to come out, he still is an utterly horrible artist. Just amazing. Heh.