Princess Luna

Princess Luna, formerly Nightmare Moon, is a pegasus unicorn pony with black skin, blue armor, and a mane of dark mist in her Nightmare Moon form, and purple skin with blue hair as Luna. She is the sister of Princess Celestia.

History
A thousand years ago, the day/night cycle of Equestira was ruled by two sisters: Luna, the younger, who brought the night, and Celestia, who brought the day. However, Luna grew jealous of her sister: the ponies of Equestria all enjoyed and loved Celestia's daylight, but were all asleep at night. No one was awake to appreciate the beautiful night she had worked so hard to create. Eventually, this jealousy and bitterness drove Luna over the edge. She became Night Mare Moon, a powerful mare with incredible magical power. She refused to allow Celestia to bring forth the sun, and planned to plunge Equestria into eternal night, but her sister, with great sadness and regret, stopped her using the Elements of Harmony, and imprisoned Night Mare Moon within the moon. She remained there for one thousand years, until she escaped during the Summer Sun Festival.

Personality
Initially vengeful upon her release, when she was defeated by Twilight and the others with the Elements of Harmony and returned to her Princess Luna for

Powers and abilities
Being one of the two Pegasus Unicorn Ponies, Nightmare/Luna possess magic far beyond normal unicorn ponies.

Appearances
S1E1: Friendship is Magic (Part 1) (Nightmare Moon) S1E2: Friendship is Magic (Part 2) (Nightmare Moon/Luna)