Chapter Text
Warning: some of the story is told from the perspective of the Joker's doppelganger, so there may be some darker content.
If you aren't familiar with the Earth 3 universe, you might want to read the summary below.
On the chaotic and dystopian world of Earth 3, there's no Justice League. Instead, there's a Crime Syndicate, composed of evil counterparts of the Justice League. In some versions of Earth 3, the roles are reversed, and weaker meta-humans and characters who would otherwise be villains work for good.
Owlman is the bad guy, and the Jokester is kind of the good guy, except he nurses a personal vendetta against Owlman and dreams of bringing about his ultimate humiliation and ruin, kind of like the Joker.
Jokester is sort of like the Silver Age / Bronze Age Joker re-imagined as a superhero, and Owlman is Batman re-imagined as a criminal.
These are official DC characters.
Jokester and Owlman appeared in the Countdown: The Search for Ray Palmer: Crime Society comic. Owlman and the rest of the Crime Syndicate also appeared in the Forever Evil story line. Unfortunately, Jokester and the rest of the Riddler Family did not appear in the newer Forever Evil story line. Instead, the Joker appeared, and it is unknown whether this Joker was once the Jokester or not.
Unlike the Joker, the Jokester does have a name and a known origin story. In the comic in which he appears, his name's Jackie. He started calling himself "Jokester" after watching Owlman brutally murder his manager Harley Quinn and getting his face sliced open by Owlman's weapon, giving him a permanent Glasgow grin. The incident made him go kind of crazy. He used some of the money he made as a ridiculously successful comedian to create a secret lair and manufacture special weapons with a clown gimmick to mock the much-too-serious super villains subjecting Gotham City and much of the world to their whims.
Owlman, of course, has a different backstory. He and Alfred conspired to kill his family so that they would inherit the Wayne fortune. His brother Bruce was against this and unfortunately also became a casualty of the conspiracy. Thomas Wayne Jr. grew to be a powerful, intelligent, lonely man who controlled crime through organizing it and bringing it under the Crime Syndicate's rule. The two people he remained close to were Alfred and his first Talon Dick Grayson.