Elves originated in the Feywild, a bright and wildly magical echo of the known world. There they were one of the azatas, outsiders that believe that freedom and goodness are the highest virtues. However, a small group of azata rebelled against the others and tried to conquer them. This group was cast out to the Material Plane where they became the Drow. The azata that would become elves then voluntered to make their home on the Material Plane as well and guard that world against the Drow.
Elves love freedom and the wild places, as befits a creature of the fey. They seek to preserve beauty and are creative to a fault. Oddly for long lived beings, they have very short attention spans and are often seen as flighty by other races. Yet they take their responsability ti guard against drow very seriously and when dealing with them they show a focus they don't have in other pursuits.