Kryppen the Poisoner is a madman who used to poison all of his victims. He was one of Arkham Asylum inmates, when Neron's evil spread throughout the world. He heard the ethereal voice of the demon and offered him his soul in exchange for power. However, Nero, first ordered him to perform few tasks.

A short time later, after entire asylum is plunged into darkness, Kryppen suddenly head-buttted Jeremiah Arkham in the nose and loudly claimed that he made a pact with the devil, causing a full-scale riot. However, Kryppen was badly beaten by guards, caught with the others and taken to his cell.

Later, he managed to suprise and killed his guards and imperceptibly got into the kitchen. He begins used his knowledge of poisons to whip up a quick cocktail that he uses to taint the hospital's cooking supplies. When it comes time to serve dinner, all of the patients begin falling over with uncontrollable spasms. Arkham himself eats a tainted cookie and falls to the floor of his office.

With all asylum was incapacitated, Kryppen called the Batman. When he arrived, Poisoner told him that he will surrender the cure so long as Batman willingly murders at least one patient. He also revealed that the corrpution of the moral code of Batman, was that the task that Nero ordered him to fulfill. Batman, who refused to play Kryppen rules, caught him and forced him to eat a sample of his own poison. As fear overwhelmed him Kryppen took Batman to the place where it was hidden cure. All patients were given medicine and Kryppen was left terrified of being discovered by the devil, who will punish him for his failure.