Who is Morgoth from The Silmarillion and what is their importance?

Morgoth begins life as Melkor, or He who Arises in Might, the rebellious Vala who creates evil and originally the mightiest of the Ainur. He is also referred to as the Dark Lord, Bauglir, the Enemy, and Belegur. He is imprisoned shortly after Elves awake, but after serving three ages, he convinces Manwe of his reformation and is released. He destroys the Two Trees of Valinor before returning to Middle-earth, summoning his evil creatures, and attempting to corrupt Elves. Once Men awake, he turns his attention to them as well. Feanor curses him and names him Morgoth after the Silmarils are stolen. After the Great Battle, he is imprisoned beyond the world in the Timeless Void and guarded by Earendil.