Jonathan Crane was interested in the study of human fears and phobias ever since he was a child. Nicknamed the "Scarecrow" as a teenager, Crane was bullied and chastised for his scrawny appearance. The boys would call him Icabod Crane, for his resemblance to the fictional character. Crane loved the character, except when he came upon the part when Icabod is disgraced by his nemesis. He was outraged by the fear that overwhelmed Icabod and swore to never expose his fears to a bully.
Crane was a Professor of Psychology at Gotham State University until his experiments in fear became too dangerous. He lost his job due to his obsession with inspiring terror in his patients and students. Crane turned to a life of evil and used various drugs, chemicals, devices, and his expertise in psychology to terrify whomever crossed his path. He took the name "Scarecrow" which the bullies gave him as a boy, and would use it to become one of the most feared criminals in Gotham.
The Scarecrow has been known to pollute Gotham's water supply with his fear toxins, infect professional athletes with his chemicals, then bet against their teams for the money to fund his evil experiments. He even had one of his henchmen spray Batman with his toxin, in the hope of driving him mad with fear. A sick and twisted man, his ultimate goal of crippling Gotham State University was foiled by Batman. He was sentenced to Arkham Asylum where he became even more dangerous by gaining criminal contacts with the likes the Mad Hatter, who also shares a sick interest in various types of mind control. These contacts would aid him in his quest to bring Gotham and Batman to it's knees with fear.
Matt Hagen was a well-known movie actor. Badly disfigured in an automobile accident, he was rushed to the Gotham burn clinic. At the clinic Hagen was approached by Roland Daggett, a crooked businessman looking for test subjects for his "miracle product" RenuYou. Daggett promised the product could restore Hagen's features within minutes as compared to the years of plastic surgery he would have to endure. The only problem was that this drug was not FDA approved and highly addictive. In exchange for the product, Daggett forced Hagen to commit crimes. When Hagen finally refused to do any more of Daggett's dirty work, the supply of RenuYou was cut off. Crazed for the drug, Hagan broke into the Renu You plant where he Daggett's henchmen poured gallons of the untested toxic chemical down Hagen's throat.
Instead of dying from an overdose, the chemical soaked every cell in Hagen's body, transforming him into a hideous man of clay. An enraged Hagen vowed to destroy Roland Daggett. What Hagen did not realize was that his new cellular structure allowed him to change his shape and appearance. He could form anything he wanted just by thinking it. As a living shapeshifter, he became the evil Clayface. As one of Batman's most bizarre and difficult criminals to handle, it takes great measures to apprehend Clayface. When caught, he was deemed insane and a special suit was designed to hold him in Arkham Asylum
Harleen Quinzelle was a brilliant and successful criminal psychiatrist. After encountering the criminal mastermind, The Joker, at Arkham Asylum, Harleen develops a fascination with the madman's maniacal psyche. She begins to treat him, only to find herself completely under The Joker's control. Unable to break his hold on her, Harley enters a world of crime as The Joker's criminal accomplice and lover, Harley Quinn.
Harley quickly becomes one of the Dark Knight's deadliest enemies, as she carries out The Joker's every evil whim. She develops a villainous friendship with Poison Ivy and the two become sisters-in-crime by virtue of their shared hatred for male domination in the criminal underworld.
Although her true personality has been subjugated by The Joker, beneath it all Harley remains a sweet lovable person. Upon her arrest, she is deemed mentally unbalanced and sent to Arkham Asylum - not as the brilliant doctor she once was, but as one of Gotham's criminally insane on the other side of the padded cell.