-- Balrogs --

I havent read all of the Silmarillion yet or maybe I just missed it but I've always been a little hazy on the balrogs.

Where did they come from exactly and what role did they play in the ealier ages?

Where there many of them and if so what happened to them?

This kind of goes with the first one but what are they exactly? Are they like the orcs in a way, a corrupted form of another race, or where they just created?

That actually brings me to another question..... from what I understand orcs and the other evil creatures were created by Sauron and Morgoth in some sort of way. If this is so, does anyone know how this was done and what they were created from? (I thought I heard somewhere that orcs were corrupted forms of elves but I'm not too sure)