DC Universe/J

Jack of Spades
Also known as Hi-Jack and the Jack of Clubs, this costumed villain was a founding member of the original Royal Flush Gang, which was put together by Amos Fortune.

Jason Todd
Jason Todd was the second individual to assume the costumed identity of Robin. He served as Batman's sidekick for a brief period before being brutally murdered by the Joker. Jason Todd was resurrected as one of the bizarre side-effects of "Infinite Crisis" and healed by Ra's al Ghul in one of his Lazarus Pits. Driven insane by the experience, Todd then adopted the identity of the Red Hood - a guise once assumed by the very man who killed him. As the Red Hood, Todd became an enemy of Batman.

Joe Chill
Joe Chill was just a common mugger who made the unfortunate mistake of holding up Thomas and Martha Wayne at gunpoint. He shot the Waynes right in front of the eyes of their young son, Bruce. The trauma drove young Bruce to pursue a life of fighting crime and he eventually assumed the mantle of the Dark Knight Detective, the Batman.

Joker
The Clown Prince of Crime. The Harlequin of Hate. He is a man of many names and even greater mystery. His true identity is unknown, but his reputation is known across the country. He is the greatest threat the Batman has ever face. An unrepentant psychotic killer, the Joker creates chaos for the sake of chaos. He cares little for money or power, and seeks only to sew discord and madness everywhere he goes. It is believed that the man who would one day become the Joker was a failed comedian, who was bribed into committing a robbery under the guise of the Red Hood. On the night of the crime, the Red Hood had an encounter with Batman. During the fight, the Red Hood fell from a catwalk into a vat of chemicals. His body was flushed out a drainage pipe into the river, but when he emerged, he was shocked to find that the chemicals had turned his skin white, his hair green and his face contorted into a bizarre jester's grin. Driven irrevocably mad, this man abandoned the Red Hood identity and became the Joker. Ever since, he has done everything in his power to make Batman's life a living hell. The Joker has been captured many times and remanded to the Arkham Asylum state institute for the criminally insane, but always manages to find a way to break free. In addition to the multitude of crimes and murders he has committed, the Joker is also responsible for killing Jason Todd (the first Robin), crippling Barbara Gordon (the first Batgirl) and fatally shooting Sarah Essen Gordon (wife of Commissioner James Gordon).