Brightroar was a Valyrian steel sword in the possession of House Lannister and wielded by the Kings of the Rock in the days before the Targaryen conquest. King Tommen II Lannister of the Rock led an ill-fated expedition to Valyria from which he did not return, and the sword was lost. In 292 AL, Gerion Lannister travelled to the ruins of Valyria in search of it, but also did not return.
Lord Tywin Lannister sought to buy Valyrian blades from lesser houses three times, but each time was rebuffed, much to his anger. Shortly before his death, he had the Stark Valyrian sword Ice melted down and reforged into two such swords, Widow's Wail and Oathkeeper, the former of which he gifted to his grandson King Joffrey I and the latter to his son Jaime. Jaime, unable to properly use the blade due to the loss of his sword hand, made a gift of it to Brienne of Tarth.