Celestia is an Alicorn and one of the two current rulers of Equestria, ruling alongside her sister Luna. During nightmare Moon's banishment, Celestia had to rule the kingdom by herself until she was turned back to normal a thousand years later.
Celestia is a very tall Alicorn, the tallest one as of now, as she is about as tall as Pearl and Kyra. As a princess, she is often wearing royal hoof shoes, tiara and necklace with a purple gem at the center of it. Her wings and horn are naturally longer than Pegasi and Unicorns. Her Cutie Mark, as she is the goddess of the sun, represents the sun.
As the ruler of Equestria, Celesia holds a standard leadership personality towards most of her subjects, mainly with a caring and understanding nature though behaving more indifferent at times. Despite her role, she has shown a slightly playful and more cheeky nature on occasions, though they aren't shown too often.
Celestia, alongside her sister Luna, became rulers of Equestria not too long after defeating Discord, and reclaiming Equestria. She kept many creatures at bay which included Lucid, Tirek, and Sombra. However, when she found Luna turning into Nightmare Moon, she had to banish her to the moon much to her dismay, and had to take the role of ruler all by herself. This lasted for a thousand years until the Mane Six reformed Nightmare Moon and Luna made her return.
During the Equestrian Games, Celestia began to take note of Rainbow Dash's worry during her performance and went off aside to see what the problem was. After explaining to her, Celestia allowed Rainbow to go back to the Crystal Gems.
She started to show concern when told of Sombra's involvement, and when realizing about Nightmare Moon, she had Twilight Sparkle sent off to help the Gems as she stayed to get her sister back. She went to the Castle of the Two Sisters to stop Nightmare Moon, wanting peace from her, but during the fight she was found and drained of magic by Tirek. She only recovered after his defeat.
Celestia got word of the Gems' mission to go to Homeworld from Garnet, and upon hearing so not only allowed them to go, but had Twilight try to spread friendship to Gem kind there as well. She also had the Elements of Harmony stay with her for the trip.
She was there to see them off once they flew off of Earth.
While not on screen, she, Blue Diamond, and Discord worked together to create a Warp Pad to connect Homeworld, Earth, and Equus together as a reward to the Crystal Gems and Mane Six for defeating the Osicone.
She and Luna go off to visit Homeworld after a meeting was called, but mainly it was because the Diamond Dogs were stealing Homeworld Gems, and Yellow Diamond suspected her for some involvement on the matter. Celestia took it in stride and easily apprehended the Diamond Dogs, presenting them to Yellow Diamond before bringing them back to Equestria with her.
During the event with the Tantabus, she entered the dreamworld herself during the ultimate dreamscape, and confronted her sister about her self-harming punishment. She made sure that they were all there for her and that they all trusted her, no matter what Nightmare Moon did.
My Little Universe: Supernova
Before the Everstorm passed through, Celestia made the ultimate sacrifice, and casted a spell on the Sun and Moon of Equestria so they could move on their own, removing her special talent and Cutie Mark in the process. she and Luna take charge in leading the residents of Ponyville out of Equestria and to the Midnight Palace. After getting settled into the area though just in the Nether Lands, she was found by the Sigbin. Seeing the Sigbin's desperation, and wanting to keep everyone else safe, she sacrifices herself to the Sigbin, allowing herself to be killed so the Sigbin could survive.
Celestia is a very powerful being when it comes to magic, and is strong enough to be able to physically move the sun of Equus. While her sister was banished, she also had to move both the sun and the moon by herself.