Jack Napier was born in Brooklyn and came to live in Gotham City. In his school years Jack proved himself to be emotionally unstable, but highly intelligent, showing aptitude in art, science, and chemistry. He also turned to a life of violent crime. When he was fifteen, Jack was convicted of assault with a deadly weapon.
Years later, as a young man at the age of 26, he and his partner in crime mugged Bruce Wayne's parents, Dr. Thomas Wayne and his wife Martha, while they were walking home from the movies. When Thomas interceded to protect his family, Napier stepped from the shadows and shot both him and Martha in cold-blooded murder. Napier pulled the hammer back on his gun and next pointed it at Bruce. Napier inquired "Tell me, kid… you ever danced with the devil by the pale moon light?". Before Napier could fire, his panicked partner urged him to leave, saying "Let's go, Jack" (which caused Napier to turn to his partner with a puzzled look). Napier decided to spare the boy and left, saying, "See you around, kid." Little did Jack know that his prediction would come true — that he and Bruce would meet again someday.
Years later, Napier became the right-hand man of the crime boss Carl Grissom, but when Carl found out that Napier was fooling with his girl, Alicia Hunt, he called Lt. Eckhardt to kill his right-hand man, who (along with his men) was trying to erase evidence of criminal activity in the Axis Chemical Factory.
Eventually, Napier meets Batman for the first time. Before he was going to escape, he kills Eckhardt after he told him to think about the future. Napier then turned the gun on Batman and caught a ricocheted bullet through his cheeks; in a panic, Napier stepped off a catwalk over a vat of a toxic chemical. Though Batman caught Napier's arm and attempted to pull him back up to safety, Napier's leather glove slipped through Batman's and he plummeted into the chemical vat below him.
Napier somehow survived and the reaction of the chemicals left him with chalk white skin, green hair and red lips. He tried to do reconstructive surgery, which severed critical facial nerves, leaving him with a wide, ridiculous and famous smile. He began to realize his insanity after looking through a mirror, much to the surprise of the surgeon. He returned to Grissom's office to kill him in revenge for his attempted murder, which he did and became the new crime lord known as The Joker. When sitting on his now deceased boss' desk, he picks up a newspaper which reads "Winged Freak Terrorizes Gotham City". Now wanting publicity and plotting to get rid of Batman, he replies with a smile "Wait til they get a load of me", and then laughs.
When he learned about Vicki Vale, the Joker fell in love with her and tried to steal her from Bruce Wayne. He made a remarkable and drastic entrance near the city hall where he killed a fellow crime lord with his quill pen. His mime henchmen then started to shoot all over the place and killing the crime lord´s aliies, with Bruce Wayne being "hit", but survived. He then heads for his limo and solemnly waves goodbye to Bruce before taking off.
The Joker begins his "parade" at the start of the Gotham City Festival that celebrating the city's 200th anniversary, bringing very hefty sums of cash to all Gotham's citizens. Along with his parade were his precious and cartoonish balloons filled with the deadly Smylex gas made from the ingredients used to create his cosmetic Smylex products. He notices Batman's Batwing up in the sky and proceeds to go as planned with his balloons. After throwing the money to everyone in the streets, the Joker wrapped up his speech saying everyone should "go with a smile".
But after Batman stopped his maniacal festivities and saved everyone from the Joker's Smylex via his Batwing, he shot and killed his right-hand man Bob the Goon, and eventually went on to face Batman while his men ordered everyone to leave the money-littered, panic-stricken streets. The Joker used his peashooter revolver and shot the Batwing down. He then found Vicki Vale near the Batwing in front of the old Gotham City Cathedral and takes her hostage (telling her "Darling, I've got to get you to the church on time.").
Batman followed them into the cathedral. While Batman battled his thugs, Joker dances with Vicki before the Dark Knight finally faces him.
During their deadly confrontation, in which they identify each other and their motivations, Batman repeatedly beats up the Joker and manages to knock him off the balcony, but the Joker reached both his arms up, and managed to pull Batman and Vicki down, themselves holding on for life from a narrow ledge while the Joker stomps and dances on the ledge in an attempt to make both of them fall. The Joker's helicopter arrived to retrieve him to safety. Batman used a grappling hook to tie Joker's ankle to a large, heavy gargoyle. Unable to break free from the heavy burden of the gargoyle, The Joker lost his grip on the helicopter's rope ladder and fell screaming to his death, hitting the cathedral's flight of steps below.
Commissioner Gordon found The Joker's body, hearing a tinny, pre-recorded laugh. He reached into The Joker's coat and pulled out a laugh box that had been activated by the landing.
Despite the Joker's reign of terror finally met to an end for good, Bruce Wayne would continue to have bad memories of Jack Napier slaying his parents for several years.
- Goon Command