Melkor a.k.a. Morgoth, Belegurth, Bauglir is an immortal Valar, a primary outset of evil in Ea and one of the most decuman creatures ever existed. Melkor was the first Dark Lord, and Sauron was a subordinate servant of him. Melkor committed plenty of atrocities. He thieved the Silmarils, that he later would inlet into his coronal, eliminated the Two Lamps and the Two Trees of Valinor.
Melkor’s generation was Eru’s doing in the Timeless Halls at the outset of Creation. From Eru he received more strength than other Valar, so he turned the most prepotent of them. He craved after creating things on his own, so he looked for the Flame Imperishable, that actually appertained to Eru, without any success though. During those searches, Melkor provided himself with rebellious ideas which were absolutely not appropriate to other Ainur. That is why he turned against Eru and aspired to pervert the world.
When Eru Iluvitar and the other Ainur sang Ea into an entity, Melkor took the decision to disobey and disrupt the music, so he sang his very own songs designed to cause repulsive things in Arda. Later, when Arda got created, some Valar come down there to improve it. Melkom descended too, but he wanted to mar good things other Ainur did. Effusions, absolute darkness, insufferable heat and coldness were among the things Bauglir was a creator of.
Melkor got himself vehemently opposed to the other Valar who had chosen his less powerful brother named Manwe and not him to be their ruler and the master of this new realm, so he fought against them and he was at an advantage for a long time. Melkor destroyed everything that other Valar did to improve the world. That is why Arda was malformed. The other Valar weren’t capable of restraining him until the Valar named Tulkas went down to Arda, and Melkor left it having fled before the power of Tulkas.
Later on, he came back and eliminated the Two Lamps, the single spring of light. Then he demolished Almaren, the land of Valar, who withdrew to Valinor. Arda was on fire and in darkness. Melkor then settled in the Northern Arda and established a lair named Utumno. Bauglir spread hatred, jealousy and other evils through the territory of Arda to deprive it constantly. Melkor also created monstrous creatures inhabiting Arda, such as goblins, trolls, Balrogs, dragons, etc. He tortured Elves having them turned into orcs. In order to help Elves, the Valar started a warfare against Melkor and beaten him. Melkor got captured. But then he got set free because he pretended to be meek. In fact, he waited for a revenge. With the help of Ungoliant, another evil spirit who had the likeness of an arachnid, he demolished the Trees named Telperion and Laurelin, thieved the Silmarils, belonged to the Noldor, and fled away.
The Noldor started a war with Morgoth to receive the Silmarils back. A lot of battles were fought right after the period when the Sun and the Moon rose up at first. After beating these parties Morgoth held a warfare against the Elven territories, has sharply reduced the domain of their realms. The Valar were asked for a support.
In the War of Wrath Morgoth got beaten by the Host of Valinor which descended to help Elves and Men. In spite of using his secret weapon, Dragons, Melkor faced a defeat and got captured, and a chain was made for him of his own crown. He pleaded for mercy and yet got put to death, he was deprived of the physical body. In the likeness of an extremely weakened spirit, Melkor was expelled into the Void, the place where he still resides.
It is believed that one day Melkor will destroy the Door of Night, set himself free and will come back to Arda. This will cause the start of the decisive combat named the Dagor Dagorath, at which Morgoth will be finally killed by Turin. Beyond that defeat, Melkor will never recover again.