Hellboy is a film based on the famous comics of Mike Mignola. The character of Hellboy, however, is completely transformed within del Toro's rendition. The character is softer and, in a sense, more sentimental.
Hellboy is a demon raised by a human man and thus he does not destroy humanity as his true nature would demand. Instead he actively protects people. In contrast with the original comic, del Toro's rendition is characterised by a tenderness between the man and demon - not only is his human father his moral compass, but also the only person that really understands the conflict inside him and the fact that he feels like an outcast.