Ardra was a devil-like figure in Ventaxian culture. The Ventaxian people considered it bad luck to say her name out loud.
During the 14th century, the planet Ventax II faced a number of crises, including war, and pollution. During this period, the Contract With Ardra was drafted, stating that Ardra would provide the Ventaxian people with 1,000 years of peace and prosperity, and at the end of which, the planet and its people would become her property.
In 2367, a female con artist took the identity of Ardra in a failed attempt to take control of the planet. Even after her exposure, she maintained the name. Starfleet officers also continued to refer to her by the name of Ardra. (TNG episode: "Devil's Due", TNG comics: "Shore Leave in Shanzibar!", "Consorting With the Devil!", "Dirty Work", TNG - Slings and Arrows eBook: The Oppressor's Wrong)