Princess Luna

Princess Luna, the Princess of the Night and Princess of Equestria alongside her older sister Celestia, is an alicorn who has a dark indigo body, an eternal dark blue mane and tail, and teal eyes. She has a large cutie mark showing a white moon in a black background, and speaks with a mild English accent. As "Princess of the Night", she possesses the ability to enter ponies' dreams and help them face their fears. She raised and lowered the moon each night, but she became jealous of Celestia because the ponies slept through the night and thus did not appreciate her work. This jealousy eventually transformed Luna into Nightmare Moon. Celestia banished Nightmare Moon to the moon after she tried to bring eternal night to the world. When Nightmare Moon escaped her imprisonment on the moon she returned to Equestria where the six mane characters use the Elements of Harmony to transform her back into Luna whereupon she resumed her place at Celestia's side.

In the alternate world shown in My Little Pony: Equestria Girls, she is known as Vice-Principal Luna, and helps her sister, Principal Celestia, run Canterlot High.