Princess Celestia

Not a whole lot is known about Princess Celestia's history aside from what is written in books. What is known is that when her sister Princess Luna became jealous that ponies were sleeping through here beautiful night, Princess Luna became Nightmare Moon, and was banished by Princess Celestia to the moon, and thus began ruling Equestria herself, taking on the responsibility of raising both the sun and the moon. On the day of the 1000th year of exile of Nightmare Moon, Princess Celestia sent her student Twilight Sparkle to Ponyville to make some friends, and set into motion a chain of events that changed Twilight, Celestia, and Luna's lives forever.

With Luna now returned to her side, and Twilight with a cadre of friends to aid in her adventures, the group work together to bring Discord to heel, defeat Sombra, Tirek, and place Princess Cadance and Shining Armor on the throne of the Crystal Empire. Later revealed to have been a friend of Starswirl the Bearded, the strongest pony conjurer of a bygone era, when Twilight Sparkle completes one of his unfinished spells, she too ascends to become a princess, the Princess of Magic.

Things in Equestria are calm for a while, so Luna and Celestia decide to step down as rules, passing the mantle to Twilight and her friends, deciding to act in an advisory role to the girls who will rule in their place. However when Sombra returns, they decide to put off the retirement to better train Twilight and her friends for their upcoming roles.

Celestia has an outwardly calm demeanor, and often much doesn't seem to rattle her, but doesn't have a problem being firm when her subjects are in danger. When relaxing, she's got a mischievous nature, and this extends to her pet phoenix Philomena as well. She's been shown to admit when she is wrong, and readily compliments those who she believes have done well. She is kind, forgiving and patient.

A tall white alicorn that towers over other ponies, Celestia has long limbs that are adorned with gold filigree on each hoof. She wears a golden collar and crown, both bedecked with a single purple gemstone that matches the shade of her eyes. Her tail and mane are constantly in motion as if a gentle breeze is blowing, but only hitting her, fluttering her pastel green, teal, purple and blue mane and tail.

When Nightmare Moon became Luna again

Defeating Discord

Twilight Sparkle becoming a princess