Ace Chemicals is one of the many locations in LEGO Dimensions 2: The Rise of Enoch, from the DC Comics franchise.
Little is known of the man who would one day become the Joker, but it is rumored that he was once a failed stage comedian who had come upon hard times. What is known, however, is that he became involved with a gang of thieves operating under the leadership of a mysterious urban legend known as the Red Hood. In truth, the Red Hood was actually several individuals, all of whom would take the point on daring thefts while wearing a solid crimson helmet to disguise their features. The Red Hood gang blackmailed this nameless comedian into donning the red helmet and conducting a robbery. The gang’s intended escape route led them through the Ace Chemical Plant.
On the night of the robbery, the neophyte vigilante known as the Batman learned of the gang's plan and intercepted them at the chemical plant. While trying to escape, the Red Hood fell from a catwalk into a vat of deadly chemicals. He managed to survive, but exposure to the chemicals turned his hair green, and his skin chalk white. It also drove him irrevocably insane. Abandoning his Red Hood identity, the man took to calling himself the Joker.
Over the years, the Joker has revisited Ace Chemicals several times, and on occasion has even used it as a temporary hideout. He once lured Batman into a trap, hoping to recreate the events that first transformed him into the Joker (with the Batman as the intended target however).