Morgoth is the dark lord who ruled before Sauron in J.R.R. Tolkien’s mythology.
Morgoth was originally named Melkor and was one of the most powerful of the Ainur, the spiritual beings involved in the creation of the world. He rebelled against the order established by Ilúvatar and became the primary enemy of the First Age.
Sauron began as one of Morgoth’s servants. After Morgoth’s defeat and expulsion from the world at the end of the First Age, Sauron later became the chief enemy of the Second and Third Ages. This makes Morgoth the earlier and more cosmically powerful figure, even though Sauron is the principal villain of The Lord of the Rings.
Morgoth’s history is told most fully in The Silmarillion. He is associated with the theft of the Silmarils, the corruption of Arda, and the wars against the Elves and the Edain. “Morgoth” means “Black Foe of the World” in Tolkien’s invented terminology.