The Last Laugh
Here are some famous last words for you:
JOKER: Sometimes I just kill myself.
And Joker does basically kill himself, although Batman helps. Joker kills himself because he puts anarchy over responsibility, and he lets his desire to kill Batman overshadow his common sense.
Instead of simply fleeing the scene of the crime after Batman foils Joker's attempts to gas Gotham, Joker kidnaps Vicki Vale and takes her to the top of one of Gotham's tallest buildings. He's waiting for his helicopter, but couldn't he have taken a car?
This is the first of a series of mistakes that leads to Joker attempting to board his helicopter without first making sure Batman is dead. As Joker clings the copter's ladder, Batman wraps Joker's legs with a grappling hook, and attaches the other end to a gargoyle. The wait of the stone statue pulls Joker to his death on the pavement below, where Commissioner Gordon finds him. The only thing still working is his creepy laughing box.
The end of the film led fans to debate whether or not Batman killed Joker on purpose, with one Redditor, as recently as 2015, claiming, "Tim Burton's Batman was a psycho who smiled when he murdered people." (Source)
Yeah. Batman and Joker are a lot more similar than either one would like to admit.
Joker wanted to reshape Gotham City into his own twisted vision, but so does Batman. In the film's last scene, Commissioner Gordon lights the brand new Bat-Signal, a device that will—you guessed it—signal Batman whenever the city is in trouble, ensuring that Gotham remains under Batman's control.
Er…did we say control? We meant caring, watchful gaze, of course.