Considered to be Batman's most deadliest foe. The Joker's origin is clouded in mystery, but one possibility is that he was a failed comedian who turned to crime to support his pregnant wife. This failed comedian met with some criminals and participated in a break in at a chemical factory and he went by the name Red Hood (because of a red helmet he had to wear) However the crime was intercepted by Batman and Red Hood jumped into a pool of chemicals to evade capture. When he removed his helmet, he realised to his shock that the chemicals had hideously disfigured him leaving him with white skin, green hair, blood red lips and a permanently etched smile. It is believed that this drove the comedian insane and he went by the name Joker.

Though his acts and appearance and even his name seem comical, The Joker is anything but that. He has killed countless number of people regardless of age, gender, and ethnic background using twisted techniques from his homemade Joker toxin to simple fire arms.  The Joker has always considered Batman his greatest foe and his crimes games to play with Batman. The Joker's battle with Batman has became personal when he crippled Barbara Gordon, killed Jason Todd (Robin II) and Sarah Gordon.

Other info
-It is believed that Joker's wife died in a freak accident involving a baby bottle heater. This happened before he his own "accident".

-The Joker has a vast knowledge of criminals and can even mix harmless agents together to make his Joker gas. He used this knowledge to escape from Arkham on two occasions.

-The Joker has tangled with other DC hero's such as Wonder Woman and Superman.

-The Joker's gas leaves a person's face twisted into a hideous grin.

-On certain occasions the Joker has had a female companion named Harley Quinn

-In the Golden Age, Joker feuded with other villains over who was Batman's ultimate villain.