In the 'Joker True Story', the Joker is the primary character. However, there could be supporting characters such as his mother (if his family background is part of the story). There may also be characters from the criminal underworld of Gotham that he gets involved with during his transformation, and even some of the ordinary citizens of Gotham whose actions or inactions might have influenced his path to becoming the Joker.
As we don't have much information on 'The Black Joker True Story', it's possible that the main character is, of course, the Black Joker. There could be supporting characters like family members who either support or oppose the Black Joker's actions. Or there could be rivals in a game or in a social setting that play important roles in the story.
Batman is definitely one of the main characters. He is the Joker's nemesis, and their interactions drive a lot of the story.
Batman would likely be a key character. He might be there to ensure that justice is served, even if it means going against the Joker's mind games.
Most likely the Joker himself. And if it follows the common storylines, Harley Quinn would also be a main character as she has a very complex relationship with the Joker.
The main character is obviously the Joker himself. His transformation from an ordinary person to the infamous villain is the core of the story.
The main character is Arthur Fleck, who later becomes the Joker. His mother also plays an important role in the story as her relationship with Arthur and her secrets impact his life.
The main characters are the Joker himself and Batman. Batman is constantly in a struggle with the Joker.
In the 'new 52 joker story', the key characters are of course the Joker, who is the central figure causing all the trouble. And Batman, who is constantly in a battle of wits and strength with the Joker. There may also be some side characters like Gotham police officers who are affected by the Joker's actions and sometimes play a role in Batman's attempts to bring the Joker to justice.
Billy Beane is a key character in the 'moneyball true story'. He was the general manager who implemented the moneyball strategy.
Harry Gordon Selfridge is the main character. He was the driving force behind the creation and success of Selfridge's department store.