Alan Moore and Brian Bolland's The Killing Joke is a graphic novel, in all forms of the word graphic. Originally conceived as an Elseworlds tale that was out of mainstream continuity, the story followed yet another battle in the endless feud between Batman and the Joker. While also serving as something of an origin tale for the Joker - featuring his time as the Red Hood that later became canon - it also was responsible for changing the life of Barbara Gordon AKA Batgirl forever. Answering a knock at the door, Barbara Gordon is stunned to find the Joker standing outside. The Joker shoots Barbara, paralyzing her, and then knocks out her father, Commissioner Gordon. When Gordon wakes up as a captive, the Joker torments him with pictures of his naked daughter, bleeding, paralyzed and further abused by the Joker and his henchmen. While the abuse occurs off-panel, Commissioner Gordon's reaction speaks volumes. Parts of this story eventually became canon, as Barbara Gordon rose to popularity as the disabled superhero known as Oracle, but it isn't ever made clear how much of the Killing Joke made it into the official history. The senseless violence and abuse shocked readers and made an impact on the overall maturity of comics.