In the Beginning
Arun and Shara are the two sleeping Titans, the creators of the first gods and the most powerful beings in Arborea.
The Titans were fleeing from a realm of endless strife. We don't know a lot about it, but legend says that they managed to escape their reality through some sort of rift, and found themselves in a void. Exhausted from their flight, they lay down and dreamed the realm of Arborea into being.
In Geography
Some say that the shape of Arborea and its continents reflects the sleeping forms of the two Titans, and that is why they bear their names - but no one knows for sure.
Dreaming the 12 Gods
In their sleep, Arun and Shara dreamed of beings of great power - which brought about the existence of the 12 original gods: Karas, Zuras, Gidd, Amarun, Tithus, Elinu, Isren, Saleron, Sikander, Dagon, Guruda and Ur.