Luna Selena Ippos is the sister of Magus President Celestia, she goes by the title/s Guardian of Night, Archmage and Vice Counselor of Canterlot, The Frigid Nightmare.
 
Luna is known to be quite the opposite of Celestia, while Celestia is known for her grace and magical ability, Luna is known for her tactlessness, and fighting ability. Though she has the same amount of magical power as Celestia, she has difficulty of controlling it. One such time is when she overused her power to the point of mental instability and paranoia for many years before being able to be treated by Twilight and her friends when she escaped confinement. She has now resumed her duties and promised it will never happen again.