In the final days of World War II, the Nazis attempt to use black magic to aid their dying cause. The Allies raid the camp where the ceremony is taking place, but not before they summon a baby demon who is rescued by Allied forces and dubbed "Hellboy". Sixty years later, Hellboy serves the cause of good rather than evil as an agent in the Bureau of Paranormal Research & Defense, along with Abe Sapien - a merman with psychic powers, and Liz Sherman - a woman with pyrokinesis, protecting America against dark forces.
| Hellboy | Ron Perlman |
| Elizabeth 'Liz' Sherman | Selma Blair |
| Abraham 'Abe' Sapien | Doug Jones |
| Prof. Trevor 'Broom' Bruttenholm | John Hurt |
| John Myers | Rupert Evans |
| Tom Manning | Jeffrey Tambor |
| Karl Ruprecht Kroenen | Ladislav Beran |
| Ilsa Haupstein | Bridget Hodson |
| Grigori Rasputin | Karel Roden |
| Sammael | Brian Steele |
| Agent Clay | Corey Johnson |
| Young 'Broom' | Kevin Trainor |
| Agent Lime | Brian Caspe |
| Agent Moss | James Babson |
| Agent Quarry | Stephen Fisher |
| Agent Stone | Garth Cooper |
| Sgt. Whitman | Angus MacInnes |
| Cpl. Matlin | Jim Howick |
| Truck Driver | Mark Taylor |
| Kid | Daniel Aarsman |
| Kid | Bettina Ask |
| Kid | Álvaro Navarro |
| Kid | Emilio Navarro |
| Kid on Rooftop | Rory Copus |
| Doctor Jenkins | Tara Hugo |
| Second Doctor | Richard Haas |
| Doctor Marsh | Andrea Miltner |
| Down's Patient | Jo Eastwood |
| Museum Guard | Charles Grisham |
| Museum Guard | Jan Holíček |
| Lobby Guard | Jeremy Zimmermann |
| Orderly | Monty L. Simons |
| Sherpa Guide | Pavel Cajzl |
| Girl with Kittens | Andrea Stuart |
| General Klaus Werner von Krupt | William Hoyland |
| Young Liz | Millie Wilkie |
| Television Host | Bob Sherman |
| Blonde Television Reporter | Ellen Savaria |
| German Scientist | Petr Sekanina |
| German Scientist | Aleš Košnar |
| Young Guy | Justin Svoboda |
| Girlfriend | Winter Ave Zoli |
| Train Driver | Santiago Segura |
| Train Driver | Albert Moy |
| Abe Sapien (voice) (uncredited) | David Hyde Pierce |
| Liz Sherman's Mother (uncredited) | Helene Maksoud |
| Guy Dressed as Dragon (uncredited) | Guillermo del Toro |
| Knight (uncredited) | Mike Mignola |
| Museum Guard (uncredited) | Miroslav Lhotka |
| Security Guard (voice) (uncredited) | Michael Lindsay |
| Radioman (uncredited) | Todd Kramer |
