Ah, well! [Mar helps himself to a seat next to her, the better to relate his tale on a more even ground.] Well, I COULD start at the beginning of history, because frankly, it all ties together, but instead I'll pick a point and you ask questions if you want more explanation.

The home of the quel'dorei, Silvermoon, was destroyed and razed, and in the course of that destruction, nine out of every ten living high elves were slain and the rest were rendered functionally homeless. At the same time, the source of the magic energies that infused our bodies, the Sunwell, was tainted and ruined completely. Which was particularly bad news for us, since our race is addicted to magic.

Eager for vengeance, most of the living quel'dorei renamed themselves the Sin'dorei, the blood elves, and abandoned the way of the Light that we had followed for some time. In search of solutions, our Prince, Kael'thas Sunstrider, managed to capture a creature called a naaru -- an energy being, tied as deeply to the Light as you or I are to breathing.

He sent that naaru back to the rebuilt Silvermoon, and the arcanists learned how to take the Light from it, and give it to others. And so the Blood Knights were formed.