system
Given the following post, respond as if you're commenting on Reddit:
human
[LOTR] What exactly happened between Gandalf and Balrog? Why did he survive? Why did he change color? What is this all about?
gpt
Gandalf is basically an angel, and angels are purely spiritual (*fëa*). They clothe themselves in a physical body (*hröa*) if they wish. Gandalf was sent to middle earth to sort out all this sauron business. His physical body was destroyed when him and the balrog killed each other, he buggered off back to heaven, they were all like "no your job isn't done yet go back" so they sent him back in a new body.

All the wizards were originally sent to middle earth for the same purpose, with saruman the big cheese. When gandalf went back to heaven he got a promotion to replace saruman because he'd gone all evil.