About 600 BBY (600 years before the Battle of Yavin), a Jedi named Allya fell to the Dark side. She was defeated, captured alive, and sentenced to exile on the remote planet and penal colony of Dathomir. She organized the inmates, and aided by her Force powers, led a successful uprising against the guards. She then learned how to tame the rancors and became ruler on the prison planet (classified in this way by the Jedi Order of the Old Republic). Allya, who had apparently repented the Dark side, taught her daughters (her direct descendants, and thus Force-sensitive) how to call on the Force by rituals and chanting. Years later, all of the females in Dathomir continued practicing Allya's teachings, following a tome Allya had penned in her old age, called The Book of the Law. The last rule in the Book of Law was "Never concede to evil" which inevitably some did, calling themselves the Nightsisters.

Over the years, Allya chose mates from her followers to father her children. She had specific terms outlined for potential mates, and the chosen men were always given a choice of whether or not to agree to marry her. The terms, should the man accept them, was that if he fathered daughters, he would be well rewarded with gifts and a position of power. If he fathered sons, he would be fed to the rancors. Any daughters she had were raised by her personally to learn the ways of the Force, but her sons were raised by other slaves to become slaves themselves.