In the beginning was Eru Iluvatar.
And he was bored. Nothingness has an odd tendency to do that to you.
It turns out that beings of limitless power and intelligence aren't usually content to sit around not using them. This came as a surprise to no one, although this was mostly likely because no one existed to be surprised.
Existence is a vital prerequisite for that kind of thing.
So Iluvatar decided, following the grand tradition of godlike beings, that he'd populate the nothingness with life. And thus were born the Ainur, a group of angelic beings with names too difficult to remember. Except Melkor, but it would be pretty hard to forget someone with a name that unambiguously evil.
True to form, Melkor turned evil and betrayed everyone. He changed his name to Morgoth - which literally means "the enemy" - because apparently Iluvatar decided that subtlety wasn't important enough to teach the Ainur.
And so Morgoth went and secluded himself from the rest of the Ainur and made himself an army of orcs and Balrogs and other things with cool-sounding names that I totally remember, fuck you. And Iluvatar looked upon his work and saw that it was rad as fuck.
And also there were spiders that one time, I think. I'm not sure, I never finished the Silmarillion.
But anyway, that's the important part.