The film was a minor box office success, and was favorably received by critics. A sequel, Hellboy II: The Golden Army, was released on July 11, 2008.
In 1944, with the help of Russian mystic Grigori Rasputin, the Nazis build a dimensional portal off the coast of Scotland and intend to free the Ogdru Jahad—monstrous entities imprisoned in deep space—to aid them in defeating the Allies. Rasputin opens the portal with the aid of his disciples, Ilsa von Haupstein and Obersturmbannführer Karl Ruprecht Kroenen, member of the Thule Society and Adolf Hitler's top assassin. An Allied team is sent to destroy the portal, guided by a young Trevor Broom, who is well-versed in the occult. The German team is killed and the portal is destroyed—in the process absorbing Rasputin—while Haupstein and Kroenen escape. The Allied team discovers that an infant demon with a right hand of stone came through the portal; they dub him "Hellboy" and Broom adopts him.
Sixty years later, FBI agent John Myers is transferred to the Bureau of Paranormal Research and Defense (BPRD) at the request of Broom and he meets the adult Hellboy and a psychic, amphibious humanoid named Abe Sapien. He learns that a third BPRD member, Liz Sherman, has recently checked into a mental hospital to protect others from her volatile pyrokinetic abilities. Despite regular visits and coaxing from Hellboy, she is determined not to return. Kroenen and Haupstein resurrect Rasputin in the mountains of Moldova and the three unleash a hellhound known as Sammael. Rasputin imbues Sammael with the power to reincarnate and split his essence, causing two of the creature's eggs to hatch and mature each time one dies. Rasputin visits Liz as she sleeps, activating her powers and almost destroying the hospital. Myers convinces her to return to the Bureau.
Sammael's ability to multiply becomes a problem, as Hellboy repeatedly kills it, dozens are born. Concluding the eggs are in the sewer, Hellboy, Abe and several FBI agents go down the sewer to destroy them. Abe is injured while looking for the eggs, Kroenen kills most of the agents. Kroenen, whose mutilated body is run by mechanical parts, shuts himself down, pretending to be defeated. Kroenen's body is brought to the bureau. FBI Director Tom Manning is angered by Hellboy's recklessness. Myers takes Liz out for coffee and to talk. Hellboy, jealous, covertly follows them, leaving the bureau unguarded. Kroenen reanimates himself and Rasputin appears at the bureau, confronting Professor Broom. Rasputin offers him a vision of the future, showing Hellboy is the agent that will destroy the world. Broom is stabbed in the neck by Kroenen and dies clutching a rosary.
Manning takes over the B.P.R.D. and locates Rasputin's mausoleum in an old cemetery outside Moscow, Russia. A team led by Manning and Hellboy enter the mausoleum, but swiftly become separated. Hellboy and Manning find their way to Kroenen's lair and defeat him. Hellboy reunites with Liz and Myers at Sammael's new nest, but the creatures overwhelm them. Liz uses her pyrokinetic powers to incinerate the Sammaels and their eggs. Hellboy, Liz and Myers lose consciousness and are captured by Rasputin and Haupstein. Rasputin sucks Liz's soul out of her body, then tells Hellboy to release the Ogdru Jahad in return for her soul. Hellboy awakens his true power as Anung un Rama, causing his horns to regrow, and begins to release the Ogdru Jahad. Myers breaks out of his restraints, subdues Haupstein, and reminds Hellboy that he can defy his destiny. Remembering his true self and what Bruttenholm brought him up to be, Hellboy breaks his horns, reseals the Ogdru Jahad and stabs Rasputin with one of his broken horns.
Rasputin has been possessed by a creature from the Ogdru Jahad. The tentacled Behemoth bursts out of his body and grows to immense size, killing him and Haupstein. Hellboy allows himself to be swallowed by the beast, then detonates a belt of hand grenades and destroys it from the inside. He whispered something in Liz's ear and she is revived. When she asks how her soul was returned, Hellboy replies that he said "Hey, you on the other side, let her go, because for.. for her I'll cross over, and then you'll be sorry'. Liz and Hellboy share a kiss.
Hellboy's film score was composed by Marco Beltrami.
Hellboy had its world premiere at the Mann Village Theater in Westwood, Los Angeles, California on March 30, 2004.
Mike Mignola, the original creator of the Hellboy character, has stated that he was "very happy" with the Hellboy movies.
The film opened in wide release on April 2, 2004 where it grossed USD $23.1 million in 3,028 theaters on its opening weekend. It went on to gross $59.7 million in North America and $39.7 million in the rest of the world for a worldwide total of $99.4 million against a budget of $66 million.
The film was well received by most critics with an average review score of 81% based on 196 reviews and an average rating of 6.8 out of 10, which earned it a "Certified Fresh" rating on Rotten Tomatoes. The summary consensus reads: "With wit, humor and Guillermo del Toro's fantastic visuals, the entertaining Hellboy transcends the derivative nature of the genre." Metacritic assigned the film a score of 72%, based on a weighted average of 37 reviews from mainstream critics.
Entertainment Weekly gave the film a "B" rating and wrote, "Pop pretensions can't undo a basic contradiction: that our hero is fighting metaphysical evil with pure, meaty brawn. Hellboy is engaging, but it's got a lot more boy in it than hell".
In his review for The New York Times, Elvis Mitchell wrote, "Mr. del Toro avidly lavishes this texture on Hellboy ... giving it a kiss of distinction. It's an elegant haunted house of a picture with dread and yearning part of the eeriness". Roger Ebert gave the film three and half stars out of four and praised Ron Perlman's performance: "And in Ron Perlman, it has found an actor who is not just playing a superhero, but enjoying it ... he chomps his cigar, twitches his tail and battles his demons with something approaching glee. You can see an actor in the process of making an impossible character really work". The film also received good reviews in the British press – for example, Peter Bradshaw from The Guardian commented amusedly on the unhistoricity of the Nazis invading Britain in the initial sequence but overall called the film "bizarre and loopy, romantic and dynamic".
Claudia Puig USA Today was less enthusiastic and wrote, "Hellboy's special effects don't offer much of anything new, its far-fetched plot leaves a bit to be desired, and there is plenty that flat-out doesn't make sense. Those unfamiliar with the comic book may leave the theater bedeviled and scratching their heads".
Hellboy was nominated for four Saturn Awards in 2005, including Best Fantasy Film, Best Special Edition DVD Release, and Best Make-Up, which it won. In 2007, Rotten Tomatoes declared Hellboy to be the 13th best-reviewed comic book film adaptation, out of 94 total. In 2008, Empire magazine ranked Hellboy 11th in their list of "The 20 Greatest Comic Book Movies".
Hellboy was released on DVD in a two-disc special edition DVD on July 27, 2004, less than sixteen weeks after it opened in theaters. Included, were video introductions by Del Toro and Selma Blair, plus a feature that allowed viewers to click during selected parts of the film to comics drawn by Mike Mignola. Other bonus features include two audio commentaries, one by Del Toro and Mignola; and the other by Ron Perlman, Selma Blair, Jeffrey Tambor, and Rupert Evans, which was recorded on April 12, 2004. The special features also include visits to the "Right Hand of Doom" set and a two-hour documentary. This DVD topped the Nielsen VideoScan's First Alert DVD sales chart and the Video Store magazine's list of top rentals for the week ending August 1, 2004, registering a total of more than a half-million units in sales.
A three-disc unrated director's cut DVD set was released on October 19, 2004. In addition to all of the features of the original two-disc set, with the exception of a new director's commentary replacing the old one, new features included Del Toro introducing 20 minutes of additional and extended scenes, a composer commentary with isolated score replacing the cast commentary, a Cast Video Commentary with Perlman, Blair, Tambor and Rupert Evans, multiple production workshop featurettes, a Comic Con 2002 Panel Discussion with Del Toro, Perlman and Mignola, and A Quick Guide to Understanding Comics with Scott McCloud.
A high-definition Blu-ray version of the director's cut was released on June 5, 2007. It contains most of the same content as the DVD set, but is missing a few features such as the video commentary and the composer commentary.