Karl Ruprecht Kroenen

Karl Ruprecht Kroenen was born in Munich, Germany in 1897. As a child, Kroenen was renowned as a musical prodigy with an angelic voice, his talent for opera quickly securing him a tour of all the capitals of Europe; eventually, however, the onset of puberty ruined his voice and ended his career. Consumed with self-loathing at the awkwardness of his body, he took to whipping himself with an oak branch, his pain quickly turning to pleasure as he did so; as he grew older, this mixture of masochism and self-hatred led to an obsession with body perfection, and from there, to surgical addiction. Over the course of his self-surgery, he removed his nails, his lips, and even his eyelids. As a result, he also took to wearing a custom-made mask to filter out bacteria and other elements that might damage his freshly-exposed tissues.
Once he had recovered, he made a name for himself as a talented craftsman and engineer, particularly skilled in the creation of clockwork mechanisms; an early success to his name was a nightingale capable of reproducing one of Mozart's arias. However, this gift was overshadowed once again by Kroenen's obsession: he believed that the fusion of clockwork and flesh would be the means by which he could attain perfection and purity.
33 years later in 1930, he met Grigori Rasputin and soon became his most loyal follower. Soon after, he joined the Nazi party and from there, the SS: ascending swiftly to the rank of Obersturmbannführer, he earned the Iron Cross for bravery and impressed the Nazi elite with his many administrative successes - including a period of stewardship over Auschwitz concentration camp. Eventually, Kroenen's many triumphs brought him into the Thule Society, an elite society of German aristocrats obsessed with the occult; his successes were no less auspicious - by the 1940s, he was the head of the Society. Here, he could serve Rasputin more directly, while also making a name for himself as Hitler's top assassin, eliminating troublesome individuals both inside and outside the party. In 1942, Kroenen was shot and mortally wounded by a Soviet soldier on the Eastern Front. Hitler not wanting his most effective assassin eliminated, tasked Rasputin with keeping Kroenen alive. With his black magic wizardry, Rasputin not only kept Kroenen alive, but granted him near-immortality. Kroenen effectively doesn't age and is immune to most physical damage. Under Rasputin's instructions, he used the resources of the Society to initiate Project Ragnarok, engineering the machinery that would conjure the portal to the Ogdru Jahad. He also accompanied Rasputin and the troops to the remote island where the summoning would take place, assisting in the activation - and defending the area from Allied troops. Though he killed a great many of them over the course of the battle, Trevor "Broom" Bruttenholm was able to throw a grenade under the portal, and Kroenen's attempt to retrieve it only resulted in him getting his hand blown off; impaled through the heart by a length of rebar from the exploding machinery, it was believed that he'd died. However, his body inexplicably vanished soon after, though the biography reports that a corpse matching his dental records was eventually found in Romania.
74 years later in 2004, Kroenen reappeared and joined Ilsa Haupstein in resurrecting Rasputin once again. After helping to unleash Sammael on the subways, he also took part in a scheme to eliminate the BPRD's leadership and lure Hellboy to Rasputin's side: when his secret workshop was raided by the BPRD, he ambushed and mortally wounded Agent Clay, before promptly switching himself off and lying down next him. Unable to resist investigating further, the BPRD took Kroenen's body back to their headquarters for an autopsy; while the now-elderly Professor Broom examined the clues that had been uncovered among his personal effects, the "dead" assassin abruptly returned to life. After a brief confrontation between the Professor and Rasputin, Kroenen stabbed Broom through the throat as revenge for the loss of his hand, killing him instantly.
Shortly afterward, Hellboy followed the trail of clues to Rasputin's mausoleum in Moscow, where he and Director Manning found Kroenen waiting in his private quarters; for the first time in the entire film, the assassin found himself effectively outmatched by Hellboy, and even deploying a spiked pit against the intruder didn't subdue him. Kroenen's part in the film ended with him impaled on one of the spikes, unable to escape being crushed under an enormous gear that Hellboy had dropped on him. In this case, Hellboy had also avenged Broom's death, as well as the countless people Kroenen had killed. 
== Powers and Abilities ==
* Defunct Physiology: A result of Rasputin's dark magic and his own extensive modifications, Kroenen has lost his ability to feel any form of pain, whether it be from multiple gunshots, getting skewered, or performing surgery on himself. He also appeared to be essentially without any form of physical needs, able to go without food, water, oxygen, or sleep; he can even "switch off" his body, appearing dead to all medical tests, only to revive with no lasting ill effects sometime later. As further evidence of his altered state of being, the blood in his veins dried up decades ago, leaving only dust in its place. 
* Cybernetic modifications: As a result of injuries sustained during Project Ragnarok, Kroenen has a mechanical left hand and a clockwork heart that he usually winds up prior to the battle, likely to prime his body for extensive physical activity. According to his biography, his spine has also been repaired with a flexible steel rod — Kroenen had likely shattered the original after being flung into a column during the Ragnarok explosion.
* Marksmanship: He's shown to possess a deadly aim, felling numerous allied troops during Project Ragnarok with only his sidearm. However, he rarely uses a gun, preferring to make use of his blades.
* Swordsmanship: An immensely skilled swordsmen, he makes use of bladed tonfa to deadly effect; this talent for bladed weapons was present even before he began modifying his body, having armed himself with retractable katar-like daggers in Project Ragnarok. Modifications have only increased his ability; as the film demonstrates, he is proficient enough to deflect bullets back at his assailants.
* Athleticism: Once again as a result of his modification, Kroenen was capable of impressive feats of athleticism and stealth, at one point witnessed clinging to a wall without using any kind of grips or claws.
* Engineering skills: Though he may not be "one of the Reich's top scientists" as the original film script proposed, Kroenen is definitely a gifted engineer and craftsman; quite apart from designing and building his own clockwork prostheses, he is skilled enough to oversee the construction of the Ragnarok Portal.
* Surgical skills: Though rarely a priority, he evidently possesses sufficient surgical knowledge to operate on himself over the course of his self-mutilation and augmentation.