What death metal band is this fromIt's Lord of the Rings lore
Essebtially Iluvatar (the big god) created a bunch of smaller gods called the Ainur because he was bored and their songs created the planet which Middle Earth was situated on. Melkor sang a different tune to the rest so was responsible for all the evil shit and disharmony in the world.
Eventually shit happens and you end up with a bunch of lesser gods being made to do shit on Middle Earth - in the tech tree of Middle Earth, the wizards (or Ishtari) are on the same power level as the Dragons and Balrogs. Sauron was one of these lesser gods who was like Morgoth's Lieutenant in being evil.
Pretty sure I got one or two of those details wrong.
Just some naming conventions.
Ainur - Comprised of the Valar and the Maiar, who are greater and lesser respectively
Istari - this refers only to the five Maiar sent to Middle Earth to guide man to defeat Sauron
Balrogs in fact are Maiar themselves, this is why their power is on par with that of the Istari.
The power of dragons varies greatly, the eldest dragons were bred by Morgoth himself and could easily best a Maiar in single combat, but some younger dragons could even be killed by small parties of elves.
OT: Melkor failed to repent after he learned why what he did was wrong, and only became more wicked.
In fact, the Ainur were very willing to forgive him, even saying that his discord had created beauty on it's own.
The hot and the cold was his doing, and his brothers and sisters marveled at fire and snow, and all of these unintended beauties. But Melkor was jealous of pretty much everyone else for almost no reason, and turned into a massive douche and pretty much ruined everything every chance he got, and eventually he was cast out because of this.