Princess Luna is a recurring character in My Little Pony: Friendship is Magic. She appears first as Nightmare Moon, her evil form. She is from Canterlot.
Princess Luna first appeared as herself in the second episode of My Little Pony. Before, for 1,000 years she was banished to the moon for refusing to lower it. During that state, she turned into Nightmare Moon, an evil alicorn that wanted Equestria to stay in night forever. Luna says that she was sad because no pony liked her night. She cast darkness through Equestria to force ponies to like the night. Her sister, Princess Celestia, banished her to the moon and saved Equestria. After 1,000 years she returned, and Twilight Sparkle defeated her Nightmare Moon state. Princess Luna then returned to her duties as the princess of Equestria. After being evil for a long time the ponies of Equestria found it hard to accept her. Finally, they did welcome her back. Her friends include the Elements of Harmony and Princess Celestia (her sister).