Princess Celestia

Princess Celestia is the Princess of the day, and primary ruler of Equestria. She is an Alicorn with a white coat and a shimmering multi-colored pastel mane. Her cutie mark is the sun.

The Cutie Map and its floating cutiemarks, as well as the vibrating butts, are secretly controlled by Princess Celestia.

Discord's rebellion against Equestria in "Twilight's Kingdom" was actually planned by Princess Celestia from the beginning, so that the secrets of The Harmony Box could be discovered.

Derpy Hooves is the smartest Pegasi in Equestria. She was sent undercover to Ponyville by Princess Luna and Princess Celestia.

Princess Celestia compulsively says things like "My wings are so pretty" when her cutie mark is touched.

Princess Luna's transformation into Nightmare Moon was caused by her anger about Princess Celestia's decision to reduce the night's length to the timespan where really everypony was sleeping.