Princess Luna

Princess Luna is introduced in the prologue of Friendship Is Magic Part 1, depicted in a series of medieval drawings with a narration that reads: “Two noble sisters who reigned together and created harmony in the land. To do so, the elder used her unicorn power to bring the dawn. The younger brought the moon at dusk.”

Nightmare Moon
The narration continues, “Thus, they brought balance to the kingdom and its subjects, all varieties of ponies. But over time, the younger sister grew jealous. The ponies played during the day the elder offered them, but slept through the beautiful night. One fateful day, the younger sister refused to lower the moon to make way for daylight. The older sister tried to reason with her, but the younger sister's bitterness transformed her into an evil, dark mare: Nightmare Moon. She swore she would plunge the kingdom into eternal night. With regret, the elder sister used the most powerful magic known to ponies, the Elements of Harmony. Using the magic of those elements, she defeated her younger sister and sent her forever to the moon. The older sister became responsible for the sun and the moon, and harmony has endured in Equestria for generations.” Following the prologue, Twilight Sparkle reads a prophecy stating that “on the longest day of the thousandth year, the stars will set her free and bring eternal night,” though Spike dismisses it as an “old pony tale.” As she composes a letter to Princess Celestia warning her of danger, an image of Nightmare Moon is reflected in a giant hourglass Twilight owned in her Canterlot home.
The prophesied day of Nightmare Moon's return is also the thousandth day of the "Summer Celebration," so Princess Celestia sends Twilight to oversee preparations for the celebration in Ponyville, encouraging her to "stop reading those dusty books" and make some friends. The events of the first and second episodes revolve around Twilight and her friends trying to defeat her by finding the elements of Harmony.

After returning to her normal form, Princess Luna feels remorse and cries at the sight of her sister. She returns to her fold, and later the two sisters join a celebration in Ponyville, where Luna welcomes a flower garland in awe and looks up at her older sister with an eager smile.

When Luna became jealous of her older sister, Celestia, Luna's heart got full of with darkness and turned into a malicious alicorn with the intention of making night eternal.

She has dark blueish purple skin tone and long flowy cosmic hair that looks like space and even looks like a little universe, she likes wearing long elegant dark dresses that accentuate her figure and really likes brushing her hair.

She might be shy at first, but then she would act silly and extroverted, excited of meeting new friends. She sleeps at daytime and stays away at nighttime.

Since she's an alicorn, she can fly and use magic. Her duty is to raise up the moon when it's night, that's why she sleeps at daytime, she can also appear into people's dreams and teleport into places she have been before.

Princess Celestia is an alicorn and the ruler of Equestria, along with her younger sister, Princess Luna. In addition to being the one in charge of raising the sun, she is the mentor of Twilight Sparkle, whom she addresses as "my faithful student." Many consider her a mother figure, as Twilight Sparkle does her best to impress her with her studies. She is the aunt of Princess Cadance and Prince Blueblood.

Princess Cadance , whose full name is Princess Mi Amore Cadenza , is a pegasus pony turned alicorn who first appears in the Season 2 finale alongside her husband Shining Armor . She is the mother of Flurry Heart , sister-in-law of Twilight Sparkle (after she married Shining Armor) and former foal nanny , the adopted niece of Princess Celestia [ note 1 ] , and co-ruler of the Crystal Empire with Shining Armor. She is also said to be a distant relative of Princess Amore , the former unicorn ruler of the Crystal Empire.

Twilight Sparkle's human form in My Twilight Sparkle is the protagonist of My Little Pony: Friendship Is Magic. She is a unicorn pony who transforms into an alicorn and becomes a princess in The Magical Mystery Cure. She is also the daughter of Twilight Velvet and Night Light, the younger sister of Shining Armor, the sister-in-law of Princess Cadance, and the paternal aunt of Flurry Heart. At the beginning of the series, Twilight and Spike move from their residence in Canterlot to the Golden Oak Library in Ponyville to study the magic of friendship. In Twilight's Kingdom - Part 2, she is granted her own castle and the title of "Princess of Friendship." She represents the element of magic. Before becoming a princess, Twilight regularly sent friendship reports to Princess Celestia.