The Joker is purely fictional. It's a creation of the imagination in the world of comics and movies. There's no real-life basis for it. The character and the plotlines are crafted to engage and entertain the audience through imaginative storytelling.
The 'Joker True Story' is likely about the origin and backstory of the Joker character. It might explore his transformation from an ordinary person to the iconic, chaotic villain. It could involve details of his troubled childhood, his experiences in Gotham City that led to his mental breakdown and his adoption of the Joker persona.