Decades ago, Hannibal King was a private detective who was hired to investigate an industrial espionage case. While King was casing a factory, the vampire Deacon Frost invaded and killed everyone there, including King, who awoke three days later in a morgue as a vampire. Horrified at what he had become, King resisted his vampiric instincts and continued to work as a private detective, taking the blood he needed from animals, corpses and blood banks. Determined to find Deacon Frost, King took a special interest in cases involving the supernatural and soon met the vampire hunter Blade, who was also tracking Frost. Although Blade instinctively hated King for being a vampire, they put aside their differences to destroy Frost, and Blade was finally able to accept King for who he was.
After his friend Douglas Royce was slain by the Eye-Killers, servants of the Darkholders, King investigated the cult's activities, ultimately learning that they were in the service of Dracula. When Dracula attempted to possess the Darkhold, King joined the Scarlet Witch and Captain Marvel (Monica Rambeau) of the Avengers in delaying Dracula while Doctor Strange removed the Darkhold from Avengers Mansion. King then joined Blade and Frank Drake in holding Dracula back long enough for Dr. Strange to use the Darkhold's Montesi Formula to destroy all of Earth's vampires. King had been prepared to sacrifice his life, but instead, Dr. Strange was able to transform him back into a human via a complete blood transfusion because he had resisted his bloodlust.
King continued as a private detective with Drake and Blade, eventually founding Borderline Investigations with them; but when the Montesi Formula weakened, King began to revert to a vampire-like state, fracturing his friendship with Blade. During a battle with the vampire lord Varnae and Bloodstorm (a clone of Dracula), King and Drake were seemingly slain when Drake's Exorcist gun overloaded; however, the explosion apparently merged them with Bloodstorm into a new host body for Dracula. Dracula ultimately drove them from his body, and King resumed his detective career. King's recent cases have included aiding Brother Voodoo and Blade against Marie LaVeau, and recovering Simon Garth, the Zombie from Lilith on behalf of Donna Garth. CIA agent Tatjana Stiles hired King to investigate the vampire Navarro, who had stolen biological weapons; but Navarro captured King, forcing him to feed on a live human by threatening to make the victim a vampire instead. King and Tatjana ultimately destroyed Navarro, but Tatjana was horribly injured. She begged King to make her a vampire in order to save her, and King gave in, taking his second human life.