Batman: The Killing Joke
This version of the Joker was a struggling comedian with a pregnant wife. He was behind on rent and had to make money somehow so he had to turn to crime. He was hired by a crew to break into Ace Chemicals and steal something. After being hired the news was broken to him that both his wife and the baby died in an accident. He didn't want to take the job anymore because of this but he didn't have a choice and was forced to wear a disguise. His disguise was the Red Hood, basically a black suit, red cape, and a red glass helmet. As soon they got there a guard spotted them and opened fire, Batman found out and arrived there shortly to resolve the issue without anymore casualties but when Joker saw him, he was frightened and tripped over the edge and fell into a vat of acid. His skin became while, lips became red, hair was green, and had a huge smile on his face.
The Dark Knight
This version of the Joker does not really have a solidified backstory, in the movie when he tells people how he became the way he is, how he got those scars, he has said that either he had an abuse father or he did it to himself because his wife had a face scar and he tried to make her feel better. He is also hands down the best Joker from any live action film.
Joker
Arthur Fleck was a comedian who was struggling with mental illness and a laughing disorder. It was later revealed that he actually was a sociopathic and eventually began to become evil because of the abuse he faced from the people of Gotham City. At one point while being assulted This lead him to become the vengeful anarchist known as Joker.
Gotham
Jerome and Jeramiah Valeska are not actually the Joker, but two different versions of him. The show Gotham did not have the rights for the use of the Joker so they had to make their own adaptations of him which turned out to be perfect. Jerome was a circus boy whos father left him and he had an alcoholic/abusive mother. All of her abusiveness drove him mad to the point where he ended up killing her, which starting an investigation in GCPD and led to him meeting Detective James Gordon, who eventually found out he killed his mother and revealed who his father is.
Gotham
Jeramiah left Jerome at a young age to have a better education somewhere else and because he felt that he was in danger being near Jerome, as he would often abuse and scare him as a child. When Jerome finds out where his brother went he eventually got to him and after a quick talk toexplain that he wanted to kill him he had to let him go because Jim and Harvey showed up. The way that Jeramiah becomes the Joker is after Jerome dies he had a package sent to Jeramiah, which said that it was from Bruce Wayne who he recently became close to, but when he opened it he was sprayed with a special mixture that Jerome had made, just for him, making him insane and turning him into the Joker.
