Entries in each category are by release date/publication date.
- "The Chained Coffin" (debut): Azzael is the father of Anung un Rama, who would become Hellboy. A powerful figure in Hell, Azzael corrupted many mortals, being known as a lord of local witches in England. Marrying the witch Sarah Hughes, Azzael later returned for her, murdering her human children and taking her to Hell where he burnt her away to retrieve his true son. Cutting off his son's hand to fit it with The Right Hand of Doom, Azzael intended on causing the apocalypse to control the Ogdru Jahad himself, and though his presence in the series is minimal, all the troubles in the series can be traced back to Azzael's monstrous nature.
- "World's Greatest Paranormal Investigator" (debut): Herman von Klempt is a Nazi scientist with an inability to stay dead, even after having been reduced to little more than a head in a jar. Herman von Klempt attempts to resurrect an old Nazi project to wipe out America with slaughterous vampires; tries to take out the spinal fluid of young peasant girls in his first meeting with Hellboy; and conducts terrifying experiments on hundreds in the depths of an old prison in Brazil. Herman von Klempt reaches his full streak of evil upon pledging his service to the Ogdru Jahad; von Klempt manipulates his granddaughter into unearthing an apocalyptic beast known as the Conqueror Worm to devour all humanity, first feeding all of her soldiers to the beast and wickedly transforming his own granddaughter into a misshapen beast to watch as he reduces the Earth to a scorched tinder and hands it over to the Ogdru Jahad.
- Issue #38 (debut, but mentioned earlier): Nimue is the Queen of Blood, and is also also known as Vivienne or The Lady of the Lake. Once a mighty sorceress who betrayed the great Wizard Merlin and imprisoned him to live eternally in his own grave, Nimue was imprisoned for 1,500 years by the witches of Britain. Upon her revival to lead the Wild Hunt, Nimue destroys the other witches of Britain and sets about marshaling an army of the Fae. When one ambassador comes to her to say his king will stand with her, Nimue forces him to murder his king, cut out his heart and forge her a new crown with it. Nimue launches vicious purges to ensure there is no threat to her rule, intending to exterminate humanity to the last man. When defeated and being dragged to hell by the witches she'd murdered, Nimue spitefully tears out Hellboy's heart to ensure she won't face damnation alone.
- The Crooked Man (issues #33-35): Jeremiah "Miser" Witkins was a war profiteer who helped to cause conflict between Natives and the colonists to line his own pockets. After being caught playing the British and colonists against one another, he was hanged and returned worse. A soul collector who makes dark bargains to obtain the souls of his victims, Witkins, as the titular Crooked Man, haunts the Appalachian Mountains, bargaining with Tom Ferrell to do evil as so many others have with his power. When Tom refuses to use his power for wickedness, Witkins has Tom's father turned into a horse and ridden to death, murdering the kind girl Cora Fisher who became a witch by sheer misfortune and lays siege to the local church with his slaves. Killing and corrupting countless innocents in the backwoods, Witkins stops at nothing to claim the souls he feels he has been owed, keeping them as hellbound slaves or gold coins he refuses to ever part with.
- The Sleeping and the Dead (issues #51-52): The Vampire Lord is a powerful vampire who helped to concoct the scheme to set most European vampires to secrecy, plotting to build their numbers and raise them centuries hence when mankind has forgotten them, allowing them to slaughter millions and take over the planet. The Vampire Lord corrupts a woman named Katherine into his vampire slave, taking her younger sister Mary as a plaything before turning her into a horrific monster imprisoned in her old house. The Vampire Lord and Katherine then prey on dozens of innocents, slowly murdering them before he attempts to raise his victims in a fury to slaughter Hellboy and the other BPRD agents.
- "The Soul of Venice" (issue #4): Romulus Diovanni was a depraved Venetian nobleman whose debaucherous parties attracted the attention of a vampire whom Diovanni befriended. Diovanni's evil exceeded even the vampire's own, and when the vampire denied Diovanni immortality, Diovanni tortured his former friend for years on end before eating him, becoming a vampire, and slaughtering hundreds. Unsatisfied with even this power, Diovanni hunts for 600 years to capture the soul of Venice's goddess Cloacina and hand her over to Shax for the power to command Shax's forces to come upon all humanity.
- Issue #19 (debut): Landis Pope is the second inheritor of the Black Flame mantle who starts out as the amoral CEO of the Zinco Corporation, unearthing the Black Flame suit for his own ends. Pope begins with the capacity for remorse and horror over what tampering with the Kartha-Hem leads to, but loses it after his seeming Disney Villain Death following his murder of Liz Sherman's homunculus friend Roger and his entire squad. Fully bonding himself to the Black Flame suit, Pope is rescued by the King of Fear and his subterranean people, where Pope repays them by manipulating and eventually killing the King of Fear in his bid to harness the Ogdru Jahad and restart humanity through them. After his death and resurrection during Hell on Earth, Pope sets himself up as a god among the survivors of New York, massacring everyone who stands up against him and shedding no tears even over the death of his loyal servant Marsten. Of all those in Hellboy who seek to use the Ogdru Jahad for delusionally well-intentioned ends, Pope stands out for ultimately throwing aside his humanity in his bid to make the Ogdru Jahad his and have them annihilate the entire planet, wreaking horrific carnage on the world at large through them before his final death at Liz's hand.
- The Bones of Giants, by Christopher Golden: Thrym was the tyrannical lord of the Frost Giants long ago. Hating Asgard beyond all reason, Thrym tortured and killed countless people in his attempt to destroy the Asgardians, eventually obliterating most of the world before being stopped. Awakened in modern day and recognizing Hellboy as containing the spirit of his Arch-Enemy Thor, Thrym devours the souls of entire towns and sets about restoring his kingdom to begin Ragnarok and wipe out the entire world to reign over what is left.
- On Earth as it is in Hell, by Brian Hodge:
- Moloch is a prince of Hell who cultivates the image of a child-devouring demon, priding himself on the "weeping of mothers" and feeding on the sacrifice of infant children. Moloch encourages his chief servant Herzog to father children solely to burn in his name and masterminds all the murder and chaos in the plot, ultimately to rein in an attack on Hell to wipe out Heaven and reduce all of humanity to become Hell's tortured playthings. Moloch even creates a sub-realm named Tartarus where his demonic servants torture and mutilate thousands of their own servants, leaving even Herzog to rot in agony as Moloch's promise of "immortality".
- Matthias Herzog is a wicked occultist and the leader of Der Horn Ordern. Allying himself with the demon Moloch in exchange for immortality and power, Herzog erects a murderous cult of Moloch devotees and revives Moloch's old ways. Fathering many children himself on women desperate for money, Herzog has them sell the babies to his cult under false pretense, sacrificing them to Moloch by burning them alive. After many of these sacrifices, Herzog, knowing full well that his master intends on torturing and slaughtering countless innocents, attempts to sell the world out to Moloch, all for the sake of his own selfishness.
- The Dragon Pool, by Christopher Golden: The Dragon King was an ancient Chinese dragon warlord that held cruel reign over thousands, devastating the populace he ruled over with fire and disasters purely for his own amusement, and forcing them to sacrifice children annually to it lest it deal worse to them. Sealed away, the Dragon King breaks out in the present day, viciously massacring the archaeological team that freed it and annihilating an entire village full of its own servitors simply for failing to provide a child to it in time. The Dragon King intends afterwards to scour the Himalayas of life, spreading its reign of terror as far as it will go.
- The Ice Wolves, by Mark Chadbourn: Carnifex, the king of the wolves, is a dark spirit sleeping within human skin. As the moon of the wolves draws close, Carnifex awakens his werewolves throughout the world, slaughtering many humans throughout. Carnifex decides to hunt the Heart of Winter and Kiss of Winter to blot out the Sun and blanket the world in Endless Winter to fully awaken hundreds of werewolves and sweep through the world to devour humans in untold of numbers, reducing Earth to a frozen paradise for the beasts eternally.
- Hellboy Animated: Blood and Iron: Erzsebet Ondrushko is an evil countess based on the infamous Elizabeth Báthory. Consumed by her vanity and wishing to stay young and beautiful forever, Ondrushko sold her soul to Hecate, the Greek Goddess of Witches. In return, Hecate transformed Ondrushko into a vampire and gave her the power to rejuvenate her body if she bathes in the blood of young women; she is said to have murdered over a thousand people in her quest to remain young. Through a series of flashbacks, we see Ondrushko take over a dress shop, by murdering the shop owner and her infant child, to lure in and kidnap a young girl named Anna. Anna's fiancé gathers a rescue party, including a young Professor Broom, which goes to Ondrushko's castle, which is filled with torture devices and the bodies of young women. Finding Anna drained of blood, they kill her to prevent her from becoming a vampire as well. Ondrushko kills most of the rescue party, but Bloom manages to kill her. Though her body died, her evil spirit remained. Sixty years later, the BPRD is sent to investigate a supposed haunted mansion, which is in fact haunted by the souls of Ondrushko's many victims. Ondrushko's minions resurrect her and she bathes in the blood in the mansion's owner to rejuvenate herself.
- 2019 film: Nimue, the Blood Queen, is a tyrant seeking the death of all humanity to build a new Eden out of the bloody ashes. Betrayed by her own coven and her body hacked apart, Nimue has a changeling named Gruagach reunite her pieces, proceeding to horrifically kill the majority of her old coven and unleash a plague upon London when she's whole again. Nimue eventually kills Gruagach after his use wears out, and after her attempt to seduce Hellboy fails, Nimue spitefully cuts the throat of his friend Professor Bruttenholm to drive him into insane rage and allow him to become the beast of the apocalypse, unleashing horrific monsters on the world through his power to horribly butcher all humanity.