Merlin

Merlin was both a powerful and important ally of Arthur Pendragon. Merlin was the daughter of both a human and a powerful Succubus. Because of her mixed blood, Merlin was able to perform many prophecies and would even train and help Arthur become King of Camelot. While Merlin had her ups and downs in Camelot with both its citizens and knights, Merlin had a complicated relationship with Morgan le Fay and Vivian, The Lady of the Lake. Because she couldn't handle Morgan, Merlin would flee from Camelot before it fell to ruin, only to then be imprisoned in a floating tower in Avalon by Vivian. Due to Avalon unique nature, Merlin is unable to both age or die unless she is freed from her tower. Because of this, Merlin now watches humanity and will continue to watch them until the very end of humanity.