Generate a question that has the following answer: Cassandra for the following movie plot: Lena, a mermaid princess, is the sea king's daughter who dreams of someday marrying a wonderful human prince. After disobeying her father, Lena visits the sea surface and falls in love with Prince Stefan. Soon after, the ship that sails the Prince Stefan sinks until Lena manages to save his life and bring him to a beach near the school where he studied. Lena comes to the aid of the sea witch Cassandra and exchanges her beautiful voice for legs to walk on land and meet her prince. Cassandra gives Lena what she asks for with the warning that if Lena fails to win the prince's heart, she will become sea foam for the rest of her life. Lena drinks the potion, loses her voice, and goes to the surface. Prince Stefan takes a liking to Lena, as he feels he should show her the same kindness that the person who had saved him from the wreck showed him. Over time, Stefan falls in love with Lena and wants to marry her, but then comes Anna, the princess who earlier found Stephan and his loyal steward Cosgrove on the beach and brought them to the medical care they needed. Stephan agrees to marry Anna, but Anna is in love with Maxwell. Vink, the dolphin pet friend of Lena, intervenes and tells the king of the sea what happened. His intervention fixes things, Anna's father King Malcolm agrees to make Maxwell his son-in-law, and Lena finally marries Stephan.
Answer:
name the sea witch?