Ouranalathra, also called "the Mistmaiden", was a female great wyrm mist dragon who once laired at Iron Dragon Mountain, in Earthfast Mountains in north Faerûn, but by 1374 DR resided at the Lake of Mists in the Endless Wastes.
In the spring of 231 DR, the Year of the Mist Dragon—a year named for her—Ouranalathra was sighted in lands all around the Inner Sea, challenging, fighting, and publicly slaying any other dragon she could find. She'd won an enormous hoard of treasure by the winter, called the "The Shining Hoard of the Great Dragon" by bards, and some several hundred adventuring bands departed from Calimport to take it. Ouranalathra spent sixty years fighting them off. She and her treasure disappeared from history afterwards.
Ouranalathra once laired at a mountain later known as Iron Dragon Mountain in the Earthfast Mountains, but later moved to the deeps of the Lake of Mists in the Endless Wastes, where she still dwelled in 1374 DR.
It is implied that Iron Dragon Mountain is named for Ouranalathra. This is explained in George Krashos's unpublished, non-canonical article, Ouranalathra, "the Mistmaiden", which tells the history of Ouranalathra, Malanthus Stormstaern, and the Master's Library. The eight mist dragons that defend the Library are also stated to be Ouranalathra's children.