The Joker is one of the main antagonists of the DC Animated Universe.
He is a notorious criminal mastermind who is the archenemy of Batman and is arguably the deadliest supervillain in Gotham City. Originally a contract killer who worked for crime boss Salvatore Valestra and his mob, the Joker fell into a vat of industrial chemicals during his first encounter with the Dark Knight - the result of which had disfigured him before he subsequently became a a maniacal gangland figure obsessed with matching wits with Batman, as well as spreading chaos and destruction along with misery wherever he goes.
To that end, he often allied himself with other villains to the point of becoming a member of the Injustice League and formerly teaming up with fellow supervillain Lex Luthor on different occasions. He is also the abusive boyfriend and employer of his sidekick Harley Quinn.
He is voiced by Mark Hamill, who also portrayed four other Batman villains, Ferris Boyle, Jordan Pryce, Tony Zucco, and Solomon Grundy in the DC Animated Universe, Fire Lord Ozai in Avatar: The Last Airbender, Arnim Zola in the Marvel Animated Universe, Skeleton King in Super Robot Monkey Team Hyper Force Go!, Malefor in The Legend of Spyro trilogy, Hobgoblin in Spider-Man: The Animated Series. Py-Ro in Crash Bandicoot, Dictatious Maximus Galadrigal in Trollhunters, Undergrowth in Danny Phantom, Darth Bane in Star Wars: The Clone Wars, Chucky in the 2019 remake of Child's Play, John Curtis in Criminal Minds, Black Phantom and Von Nebula in Lego Hero Factory Breakout, Dr. Pullum in Dan Vs., Popsicles in The Powerpuff Girls, Skeletor in Masters of the Universe, Adolpho in Loonatics Unleashed, Dr. Stankfoot in Zevo-3, Alighiero Alighieri in Dante's Inferno, Kavaxas in Teenage Mutant Ninja Turtles, Abraham Kane in Motorcity, Maltruant in Ben 10: Omniverse, ShiverJack in Jake and the Never Land Pirates, Megatronus Prime in Titans Return, Trickster in The Flash (as well as his Arrowverse incarnation), Stickybeard in Codename: Kids Next Door, British Taxi in Regular Show, Flint in Buzz Lightyear of Star Command, Niju in Balto II: Wolf Quest, General Vostok in The Real Adventures of Jonny Quest, Apep in The Scorpion King: Rise of the Akkadian, Birthday Bandit in Teamo Supremo, and Adrian Ripburger in Full Throttle.