Arnold Etchinson (also known as Abattoir) is a serial killer who grew up convinced that his family members were evil. In result, he eventually murdered them believing that their deaths would protect the world from further perils. Etchison also believed that he absorbed the life force from each victim after his or her death.
History
A serial killer who was convinced that his family was evil, Arnold Etchinson believed that he absorbed something of their life force when he killed them. He was apprehended and incarcerated in Arkham Asylum. He escaped several times and was usually recaptured by Batman; the last time he escaped was when Bane set all the inmates free in the Knightfall storyline, and he went on to kill several more members of his family.
Eventually he was tracked down by Jean Paul Valley, who was acting as Batman at the time. Valley chased him into a refinery and nearly knocked him into a vat of molten metal. Abattoir was hanging from a chain above, barely able to hold on, but Valley allowed him to fall to his death, to Robin's horror. The reason for this was given that Valley had a conflict of conscience due to his mental state. St. Dumas, the angel in this case, asked him to cast his grapple and save Abattoir, whilst his father, the devil in this case, asked him to throw a shuriken and kill him, so Valley did neither. Since Abattoir was holding Graham Etchinson inside a secret, hidden torture chamber at an unknown location, Valley indirectly condemned that prisoner to death, though he was unaware of it until Police Commissioner James Gordon informed him. It was also the main factor in Bruce Wayne taking back the mantle of Batman.
Abattoir returned as a ghost (during a brief period of increased supernatural activity, worldwide), to torment the original Batman (Bruce Wayne) using Valley's Batman-armor, but Batman proved much less susceptible to psychological assault than his substitute. Batman tricked Abbatoir's ghost into abandoning the armor and his mission. (The ghost was attempting to cause his last remaining blood relative, a pregnant cousin, to miscarry and then he would possess the infant.)