Cassilda is a character created by Paizo Inc in 2017 for the Pathfinder roleplaying game.
Background
Queen Cassilda (aka, the Queen of Carcosa) is the former queen of the city of Yhitll. She is a beautiful woman who was transformed into a life-sized hollow porcelain doll. Her tragic story is one of horror and defiance against the fate befallen her people.
During a time of upheaval on her world, her city was visited by Hastur's servant, the Pallid Mask. Whom claimed that he could help them avoid the prophecy that foretold their doom by Hastur. The nobility of Yhtill were deceived into attending a masquerade where the Yellow Sign was present, thinking themselves immune. At the given time, all of the attendants removed their masks, at which the Pallid Mask revealed his deception. He called upon the Yellow Sign, and the city of Yhtill was struck by a wave of madness, resulting in its consumption by Carcosa.
Cassilda looked away, and therefore was neither driven mad nor was she enslaved. She absorbed a portion of her peoples' tortured souls into herself, preserving their lifeforces so that one day her people may be restored. Their memories and personalities are contained within her imperial diadem. She became Carcosa's first denizen and acquired a form of immortality. As long as Hastur existed, she would continue to reform, no matter how many times she is killed. She lives for the day that Hastur is permanently destroyed and both her and Hastur are ever destroyed within 24 hours of each other, the souls contained within the diadem will either be resurrected in a new Yhtill or they will move on to the afterlife.