Catrina

Lady Catrina was a noble of the House of Tregor, and friend of Gaius. As a child she was treated by Gaius, because she had an incurable bone disease that made it difficult for her to walk. Apparently she met the Pendragon family at some point during her life.

Later a female troll assumed her appearance, who managed to enter Camelot's court and became Queen of Camelot by placing Uther under a spell. It was said that the real Lady Catrina was the last survivor of the House of Tregor. The troll stole the badge of her family to enter Camelot, but didn't know about the bone disease of Lady Catrina. This was a fatal mistake for the troll as her deception was uncovered by Gaius and Merlin before she was finally killed by Arthur. It is unknown whether the real Lady Catrina is still alive and living somewhere else or if she passed away at some point. According to Gaius, Catrina was a kind and gracious woman.