Melkor

Melkor was created by Eru Iluvatar in the Timeless Halls, at the beginning of creation. His brother was Manwë, although Melkor was considered by some to be greater in power and knowledge than any of the Ainur.

Impatient with the emptiness of the Great Void outside the Timeless Halls and desiring to create things of his own, Melkor often went forth into the Void in search of the Flame Imperishable. But Melkor never discovered it. He continued to search however, and as such was often alone and apart from his fellow Ainur. It was during these lonesome periods that Melkor began to have ideas and thoughts of his own that were not in accordance with his fellow Ainur.

When the Ainur sang the Great Music before Eru, Melkor wove some of these alien thoughts into his music, and straightaway Dischord arose around him. Some of those nearby attuned their music to his, until two musical themes were warring before the Throne. To correct the Dischord, Eru introduced a Second, and then a Third Theme into the music. But Melkor succeeded in holding back the Second theme, of which Manwë was the chief instrument. The Third was the theme of Elves and Men, and while it was not overwhelmed by the Dischord as the Second theme was, it too failed to correct it. When Eru brought the Music to an end, he rebuked Melkor, praising his strength but reminding him that, as an aspect of his creator's thought, anything that Melkor could bring into being ultimately had its source within Eru himself. As such, even the Dischord redounded in the end to the glory of Eru's work. This rebuke shamed Melkor, but brought on anger in him as well, though he hid it. Thus when the Music was made incarnate as Arda, it was already flawed through the Dischord, and immoderate heat and great cold stalked it. Melkor then took in the interest of the World and descended to it with the other Valar.

From there, he began to subtly corrupt the world. Some elves were led astray and became orcs. Other Maiar, lesser Ainur like the Istari, became balrogs or other demons. Melkor turned one such maiar into his lieutenant, a powerful Maiar named Sauron. They corrupted creation, created monsters, and ravaged the land in both magic and through wars. Melkor was eventually defeated by the Valar, powerful Ainur, and the elves. He was defeated and cast out of the world at the end of the First Age. His lieutenant, Sauron, eventually took up the mantle of evil and that persisted until the end of the Third Age, a story you are somewhat familiar with, though it has become corrupted through the Fourth.

To hear the name Melkor, who was renamed Morgoth so long ago that the name Melkor was forgotten by even his followers and should have never been uttered again in Middle Earth, is dire indeed. It means his influence has reached such height that he may return to Arda. If he does, he will begin Dagor Dagorath, the Battle of Battles. It could mean the end of Arda, of time itself.