She was the cornerstone of Ventaxian theology. She provided punishment for bad behavior and was known for making disproportionally bad deals. It was bad luck to speak her name out loud.
According to legend, the Ventaxians were granted a thousand years of peace in return for becoming Ardra's slaves and having their riches given to her. This was agreed upon and detailed in the Contract of Ardra, which was studied by Ventaxian scholars. In fact, the deal was created by Ventaxian leaders at the time to get consensus among their people.
In 2367, she was impersonated by an interstellar con artist. This impostor deceived the Ventaxians into believing she was the deity by using technology to mimic various phenomena believed to herald Ardra's return. Her ruse was revealed by Captain Picard when Lieutenant Commander La Forge discovered her ship in orbit, which was commandeered by the USS Enterprise-D's crew. (TNG: "Devil's Due")