Helena Ravenclaw was the daughter of Rowena Ravenclaw, one of the four founders of Hogwarts School of Witchcraft and Wizardry. She is known for her intelligence and was said to possess a beautiful diadem that enhanced wisdom. Helena eventually became a ghost, known as the Grey Lady, after fleeing with her mother's diadem. Her story is intertwined with the history of Salazar Slytherin and Godric Gryffindor, as well as the founding of Hogwarts. Helena's diadem later became one of the Horcruxes created by Tom Riddle, also known as Lord Voldemort, making her a significant figure in the Harry Potter series.