Once the dark elves of the world lived in the enourmous realm beneath the surface world called the Underdark. There they lived apart from the surface races, warring with the other elven races on the surface and worshipping their dark spider goddess, Llolth. Everyone knew how evil the dark elves, or Drow, were.
They were cast down by the elven god Corellon Larethian for rebelling against him together with their goddess. He banished them to the world under the world and gave them their dark skin and white hair as punishment.
And there they would have lived today, if it were not for The Destruction.
When The Destruction happened the Underdark was flooded by water and they had to flee to the surface world. There they found a world in complete chaos, besieged by Devils pouring out from rifts leading to the Infernal Hell. The dark elves rallied the other races against the Devils and with their skill and power the races of the world managed to throw the hellish spawn back to their realm. Using their mighty magics the drow and some of the other races managed to create a magical barrier that was called the Silver Shield, and they helped create an druidic organization called The Circle of the Silver Shield to protect and maintain the barrier for all time.
Since then the dark elves have found their place on the surface, working to guard the barrier and keep the world safe. Since their goddess was destroyed in the destruction they no longer worhip her, and the fascination with spiders that once was an integral part of their culture has disappeared. They are still evil, but the other races have profound respect for the dark elves, knowing all to well how important they were in saving the world and how important they are in keeping it safe.
The third child in every family is Kerrashin, "The Chosen". The Kerrashin are bound to serve the Circle, and thus many in the Circle are dark eleves.