The Joker is Luke Skywalker

How can I say this? How can I say one of the greatest science fiction movies never happen? Easy, with a heaping helping of insanity. See, it all happened in the Joker's mind. Before the Joker was the Joker he was an out of luck guy trying to be a comedian while trying to support his wife and unborn child. So he strikes up a deal with two mobsters to hit the Ace Chemical Plant while the Not Joker-Joker goes as the Red Hood. Then before he does the job he learns that his wife and child have been killed due to a defective hot plate. This is when he breaks mentally. In Star Wars, when Luke goes to find Ben Kenobi for some reason he comes back and finds Aunt and Uncle Expendable in a charred wreckage of their dirt home. Now the Joker sees all cops as nameless faceless entities of authority, namely Stormtroopers.

With nothing left to lose and a lot of comedic vengeance to wrought he goes on with the plan the mobsters set up, except now he sees the mobsters as a kind old hermit with magic powers and a light based cutting implement. So he goes to it and meets the “terror” of Gotham, or as he sees it the universe, Batman, who he now sees as Darth Vader, a robotic puppet of manipulated feelings and misery from his past. Once Batman accidentally causes Not Joker-Joker to fall in chemicals and causing him to be the Joker, he sees this as a major change in himself so he visualizes it as losing his hand. Why do you think Luke becomes such a badass in the third film? Outside to counteract the Ewoks. Now Joker does not blame Batman for this, just like Luke does not blame Darth, they both just see his adversary as a pawn in the game of the bigger evil. An old man in a position of power but doesn't have the terror factor to make worlds or cities bend to his will, i.e. Commissioner Gordon and The Emperor. 

So that is how Joker is Luke Skywalker. Chewie and Han Solo in the Joker's mind is a old fur coat and a VHS box of Indiana Jones. Leia is Harley Quinn. Also it doesn't help that they both are played by Mark Hamill.