Elements of Harmony

The Elements of Harmony are a set of gemstones which are very powerful if used by the right person. There were five known elements, loyalty, kindness, generosity, laughter and honesty. There was one unknown element, which was the element of magic. These elements were used against Luna by Celestia to imprison her in the moon. On the night Luna escaped, she found the elements of harmony and destroyed them. But the pieces went inside Twilight and the other five ponies. Therefore:

Twilight Sparkle - Element of Magic

Applejack - Element of Honesty

Rainbow Dash - Element of Loyalty

Pinkie Pie - Element of Laughter

Rarity - Element of Generosity

Fluttershy - Element of Kindness

They used the elements of harmony to fight Nightmare Moon. Nightmare Moon turned into Princess Luna and she became good again. The elements of harmony were also used twice to fight against Discord.

SHINING ARMOUR

Shining Armour is a unicorn and Twilight Sparkle's brother. He works as a the captain of the Canterlot Royal Guard His cutie mark is like a coat of arms. He is given the title Prince by relation from Princess Cadence.

PRINCESS CADENCE

Princess Cadence is an allicorn who rules over the crystal empire. She is the niece of Princess Celestia. She used to babysit Twilight Sparkle. This is what they used to chant :

"Sunshine, sunshine,

Ladybirds awake,

Clap your hooves and

Do a little shake."

She is Shining Armour's wife. Her cutie mark is a crystal heart. 

PRINCESS LUNA

Princess Luna is Celestia's little sister. She controls night. Her cutie mark is the moon. She felt very angry towards all ponies because they used to frolic and play all day long, but at night they would all curl up and sleep. So she became evil and also became known as 'Nightmare Moon'. But Celestia used the elements of harmony to imprison Luna in the moon. She also became known as the 'Mare in the Moon'. But then a prophecy was made that on a specific day she would be released from the moon. Twilight Sparkle and five of her friends helped Luna turn good. She is still very remorseful.

PRINCESS CELESTIA

Princess Celestia is the current ruler of Equestria. Her palace is situated in Canterlot. She is an allicorn. Her sister is Princess Luna and her niece is Princess Cadence. Her cutie mark is a sun and she controls daytime. She is Twilight Sparkle's teacher. She has a pet phoenix called Philomena.

Spike

Spike is a baby dragon. He was hatched from an egg which Twilight cracked open in the test for Princess Celestia's Magic Academy in Canterlot. He is Twilight's helper and was initially jealous of Twilight's pet, Owlwicious. He has a baby phoenix for a pet, called Peewee. He has a not-so-secret crush on Rarity. He loves eating gems.He is purple in colour with green spikes, green eyes and green spots. He and Angel (bunny) are kind-of enemies. 

Fluttershy

She is as her name suggests, a shy pegasus. She hates flying and prefers to live on ground. She loves animals and her little cottage is filled with them. But the most exclusive of them is a little white bunny called Angel. Her cutie mark is three butterflies. She is the element of kindness in the elements of harmony. Her greatest power is 'The Stare' by which she even tamed the cockatrice, which can turn people to stone with a single stare. She even helped Discord become good.