Hellboy is a character-driven comic. The movie has followed suit. Mignola and del Toro chose all the actors for their abilities and physical resemblance to their comic-book counterpart. The result is an ensemble cast that drives this adaptation to the level of impact of its source.
"John Hurt as Broom looks exactly like the character in the comic book. At times I thought I must have looked at a photo of Hurt when I drew this guy. It was spooky." - Mike Mignola , Hellboy creator