"The shadow of The Master covers this world...His never-blinking eyes peer into the hearts of mortals...I am his instrument, and all shall bend to me."
Nightmare Moon, also known as The Lady of the Night is one of the few remaining Alicorns, the sister of Celestia, and the matron of the night. Originally known as Luna, she was a loyalist Alicorn serving alongside her sister in the Hundred Years War. However, afterwards, her youth and brashness allowed her to harbor dark emotions, which led to their exploitation by the Dark Gods. She was corrupted by the god of darkness, Nezoth. However, she retained her awareness, but now blinded with hate and rage for all creatures of light. During what was known as the War of Nightmares, Luna led her Dark minions against Celestia and her kingdom.
Though the cataclysmic conflict did much damage to the world as well as the hearts of those who once loved Luna, Celestia included, the period of strife ended when Celestia and Blue Team combined forces for the first time, and managed to defeat the mad princess. The Nightmare ended, and Nezoth's influence over Luna ended, turning her once more into the benevolent Princess Luna.