In 1944, the Nazis constructed a dimensional portal off the Scottish coast, seeking to unleash the Ogdru Jahad, a race of monstrous entities imprisoned in another realm. With the guidance of Russian mystic Grigori Rasputin, they aimed to summon these creatures to turn the tide against the Allies, believing such chaos would lead to a new paradise. Rasputin opened the portal with the help of his followers, Ilsa Von Haupstein and Obersturmbannfuhrer Karl Ruprecht Kroenen, who was a pivotal figure in Hitler’s inner circle.
An Allied task force, led by the knowledgeable Trevor Bruttenholm, was dispatched to thwart their plans. In the ensuing confrontation, the German team was eliminated, and the portal was destroyed, tragically absorbing Rasputin in the process. However, the destruction unleashed a baby demon with a mysterious stone right hand, which the team dubbed Hellboy.
Fast forward sixty years: Hellboy's relationship with Bruttenholm has evolved, with Hellboy affectionately referring to him as "father." Unfortunately, their bond is strained due to Hellboy’s frequent defiance of orders, which jeopardizes the Bureau's reputation. Enter FBI agent John Myers, who is assigned to the Bureau of Paranormal Research and Defense (BPRD) at Bruttenholm's behest. He encounters Hellboy and meets a psychic amphibian named Abe Sapien. Meanwhile, another BPRD member, Liz Sherman (Selma Blair), has checked into a mental health facility, hoping to protect others from her unpredictable pyrokinetic powers. Hellboy's feelings for Liz complicate matters as she seems to be attracted to someone else, sparking his jealousy.
In a dark turn of events, Kroenen and Haupstein succeed in resurrecting Rasputin in the rugged landscapes of Moldova. Together, they unleash Sammael, a hell-hound capable of multiplying itself, growing stronger with each defeat. Meanwhile, Rasputin invades Liz's slumber, tipping her powers into volatility and nearly wreaking havoc within the hospital. After much coaxing, she reluctantly returns to the Bureau.
Tragedy strikes when Bruttenholm is diagnosed with terminal cancer, with only days to live. He sends Hellboy and Abe on a mission to retrieve and destroy Sammael's eggs before it’s too late. As they face off against the multiplying hell-hound, things intensify, leading to Abe sustaining injuries and Kroenen launching a lethal attack against an FBI agent. Kroenen, whose body is a twisted assemblage of mechanical parts, pretends to retreat after an encounter but is secretly plotting. As Hellboy struggles with jealousy over Liz, who is out with Myers, Rasputin reanimates Kroenen and confronts Professor Bruttenholm, offering the professor a glimpse of a dark future where Hellboy becomes the harbinger of destruction.
In a fit of rage, Kroenen murders Bruttenholm, leading to Hellboy and the attack team being guided to Rasputin's hiding place in a Russian cemetery. Here, a fierce battle ensues where Hellboy reunites with Liz and Myers, ultimately leading to Liz unleashing her fiery powers against the Sammaels. After the trio is captured by Rasputin, he forces Hellboy into a catastrophic decision: release the Ogdru Jahad or watch Liz perish. In an intense moment of self-realization, Hellboy awakens his true potential as Anung Un-Rama, regrowing his horns but ultimately rejecting his destiny.
In a climactic confrontation, Hellboy stabs Rasputin, who becomes possessed by the monstrous Behemoth. Choosing sacrificial heroism, Hellboy detonates grenades, obliterating the creature from within. When Hellboy returns, he finds Liz's life hanging in the balance. Drawing upon an emotional plea, he negotiates her release from the other side, leading to a heartfelt reunion. As they share a kiss, enveloped in flames, their bond is solidified amidst the chaos, while Myers stands witness to their love amidst turmoil.
