The Lazarus Pit is a natural phenomenon of mythical vats of arcane chemicals most commonly used by Ra's al Ghul to ensure his longlevity and eternal youth. The substance that fills each pit is a chemical blend of unknown composition, seemingly originating from somewhere within the Earth's crust, it bubbles to the surface only at certain key points around the globe, typically at the junction of ley lines.
Although capable of healing any injury, restoring youth and even restoring life, the pits have the temporary side-effect of casting the dweller into temporary aggressive insanity. Although this affect does wear off after a short time.
Ra's al Ghul, then an unnamed doctor, accidentally discovered the first Lazarus Pit as a cure for the dying son of a sultan. However, the pit's side-effect caused the prince to kill the doctor's wife.
After being blamed for the murder, the doctor was buried in the desert. Rescued by a tribe and a boy named Huew, the doctor used the Lazarus Pit to save himself, and vowed to avenge his wife. The doctor gave himself the title Ra's al Ghul (The Demon's Head).
In addition to Ra's, the fanatical terrorist cult known as Kobra analyzed and duplicated the chemical composition of Ra's pits to create an additional network of pits for their own use, while other people, such as Jason Todd, Black Canary (Dinah Laurel Lance), Riddler (Edward Nigma), Batgirl (Cassandra Cain), Lady Shiva (Sandra Wusan), Joker, Nora Fries, King Snake, Duela Dent, Wonder Woman (Diana Prince), Batman (Bruce Wayne), Batwoman (Katherine Kane) and Bane, have also used the pits at various times.
Although the Pits could initially be used by only one person and only once by that user. Ra's al Ghul's daughter, Nyssa Raatko, found a way to remedy this and manipulated the Pits for endless use.
After a mass destruction of the Pits, thanks in part to Batman (Bruce Wayne) and Bane, only five are thought to remain. One is owned by Nyssa Raatko, one lies in the Batcave (created by Bruce Wayne after he learned that the Pits were necessary to maintain the stability of the world), another in the Himalayas, one in the Australian Outback and one in Tibet.
All who have used the Pits have succumbed to the temporary side-affect of madness, except for the Joker. Who, after using a Lazarus Pit, was temporarily brought into sanity, and expressed remorse for his many crimes.
The concept of the Lazarus Pit was first developed by Denny O'Neil and Neal Adams.