“This city deserves a better class of criminal.”
Probably the most famous Joker comic of all, The Killing Joke is essential to understanding the character. On the other hand, it’s rightfully been criticized for its treatment of Barbara Gordon, which even its writer, Alan Moore, says went too far.
This story centers on Robin’s search for his mother, but is mostly remembered for its end, where he’s killed by the Joker. It’s especially memorable since Robin’s death was decided in a poll of apparently bloodthirsty comics readers.
The 2005 retelling of the Joker’s original appearance establishes him as a villain bent on sowing chaos, rather than a mere criminal. It’s not the first comic to do so, but it may be the Joker’s best origin story.
Soft Targets focuses on the toll the Joker’s violence takes on ordinary Gotham City citizens and shows just how terrifying of a force he is to people who aren’t wearing capes and masks.
Endgame is meant as the final battle between Batman and his nemesis, in which the Joker outsmarts Batman and poisons all of Gotham City. This story shows that the Joker is as capable as he is terrifying, and works as a fitting ending to his story.