Sola

Sola, also known as Queen Sola, is an immensely powerful Alicorn who is believed by most ponies to have created Equestria, and the entire world. She lives in Solos, another plane of existence which the Sun serves as a portal to. She is believed to be the manifestation of harmony, and is the creator of the Elements of Harmony.

History
Early ponies in Equestria were visited by Sola, who granted the Unicorns a spell which would allow them to control the Sun. After the Hearth's Warming Eve story and the creation of a unified nation of all the pony races (the beginning of the Classical Era), the ponies asked of Sola and Lycan, the Alicorn of the Moon, to lead their nation. Instead of ruling themselves, the two had children who they named Celestia and Luna, and assigned them as the princesses of Equestria.

For a time the world was ruled in perfect balance between Harmony and Chaos, which allowed everyone to live peacefully, but with enough chaos to make their lives exciting. One day, however, the Draconequus decided to rebel against Sola and Lycan, and managed to kill Lycan. Discord, one of the Draconequus, absorbed the Alicorn's power and went on a rampage throughout Equestria. Sola created the Elements of Harmony, and gave them to Celestia and Luna who managed to seal Discord in stone.

Sola then disappeared from history entirely. Some believe that she died in the creation of the Elements of Harmony, while others believe she is merely mourning the death of Lycan for thousands of years and will eventually return.