The one line Batman has sworn never to cross is that of taking someone's life. No matter how bad a villain is, Batman refuses to use lethal force against them. This is one of the reasons the Joker enjoys fighting Batman so much, as he tries to push Batman to break that one rule. So far the Clown Prince has been completely unsuccessful, which is all the more ironic considering one obscure villain got Batman to break his rule over 30 years ago.

Batman has dealt with many terrifying villains over the years, but only Deacon Blackfire pushed him to break his number one rule of never killing someone in Batman: The Cult #2 by Jim Starlin, Bernie Wrightson, William Wray, and John Costanza. Deacon Blackfire takes over all of Gotham, killing the mayor, the deputy mayor, and nearly killing James Gordon. Part of what allows him to take over the city so completely is by brainwashing Batman and bringing him over to his side.

Blackfire turns Batman into his willing minion, and the full consequences of this is shown when Blackfire sends Batman and a group of underlings to murder some mafia members standing in Blackfire's way. Batman kills with few issues: he guns down the man while in a drug haze and never really makes amends for it.

Related: Batman Finally Admits Joker Was Right About the Bat-Family

Batman Is Responsible for Killing a Man

No matter how bad things get, Batman always refuses to kill. But when his mind isn't his own, those rules loosen. Batman's fear of killing began as a young boy when he saw his parents shot in Crime Alley. This instilled in Bruce a deep fear of both guns and death in general. No matter how absurd it is or how difficult it is, Bruce will not only go out of his way to avoid killing people, but he'll try to save them as well — even if they're horrific villains put in danger through no fault of Bruce's. This is one of the biggest things that makes Batman a true hero, but it's also why it's so shocking when he finally does cross that line.

Deacon Blackfire spends days indoctrinating and drugging Batman until Bruce's mind simply breaks, and he surrenders to Blackfire's will. Because of this, Blackfire sends Batman to deal with some mobsters, and Batman does so gladly. The most concerning part is that Batman's inner monologue describes how great it feels to finally let loose and just gun people down. While it's well known that Batman wants to kill the Joker, readers have almost never seen the Dark Knight not only engage in lethal force but absolutely revel in it.

Batman Admits He's One of the Deacon's Men

Batman eventually retakes Gotham from Deacon Blackfire, but he not only kills someone in the process, he also allows several civilians to die, as he was completely unable to save them. When Batman finally confronts and defeats Blackfire, he lets Blackfire be torn apart by his own men who had lost faith in the Deacon after his defeat. This shows that, unlike the Joker, Deacon Blackfire manages to push Batman to break his biggest rule in every conceivable way.

Batman: The Cult #2 is available now from DC Comics!