Morgoth, once named Melkor, is the primary antagonist of The Silmarillion, and the master and predecessor of Sauron, in-turn eponymous primary antagonist of The Lord of the Rings History.
Once part of the Valar (Archangels), Melkor became the first Dark Lord who was named Morgoth Bauglir in Beleriand and Middle-earth. He became greedy and hungry for Light, but seeing it was inaccessible to him, he turned to Dark, coveting it and, by seducing many Archangels and angels and corrupting them for his course, he filled Dark with a fear for all future life. Melkor marred the Great Music of the Valar with his selfish ambitions and inspired fear and corruption amongst his brothers and sisters. Eventually, Iluvatar, God, rebuked Melkor for his pride, and reminded him that pride was his weakness. Ashamed, Melkor withdrew, but when Iluvatar showed the Valar His new creation: Earth, Melkor longed to possess it. He gained a foothold on Earth's newly created surface and fell into battle with his brethren, which lasted all through Earth's early history. Eventually, Melkor claimed Kingship over Earth and declared himself god of the realm, but it took the combined efforts of Elves, humans, Valar, and all the Free Peoples of the world to defeat him. The Valar captured him and thrust him through the Door of Night bound in a great chain, Angainor.
Amongst the Maiar (angels) that Melkor corrupted was Sauron, who was the greatest Maiar that has been created. Sauron became most like Melkor in corruption. Melkor handed some of his powers to Sauron to corrupt and govern Earth, but Sauron was not defeated until some 3500 years after Melkor's defeat. Melkor's lies and illusions live on in the souls of humans and Elves, who have inherited the world, & takes shape in men as the fear of death. Death began as a gift to humans from Illuvatar, allowing them to separate from the world & go to astral parts unknown (possibly Eru's original inhabitance, where the Valar dwelt before coming to Valinor as Ainur), which elves cannot do as they are bound to it eternally. He warped this gift to be perceived as a curse and an insult, as if immortality had been stolen from Men. Sauron later uses this to his advantage on the Numenorians.
Powers and Stats
Tier: At least 4-A, likely 3-B | At least Low 2-C
Name: Morgoth, Melkor
Origins: Lord of the Rings
Age: As old as the universe itself
Classification: Vala, Dark Lord
Powers and Abilities: Superhuman Physical Characteristics, Magic, Telepathy, Telekinesis, Immortality (Types 1 and 2), Energy Manipulation, Elemental Manipulation, Reality Warping, Curse Manipulation, Shapeshifting, Illusion Creation, Weather Manipulation, Forcefield Creation, Mind Manipulation, Weapon Mastery, Various others
Attack Potency: At least Multi-Solar System level, likely Multi-Galaxy level (Was initially the strongest of the Valar by a significant amount, caused the other Valar to flee Middle-earth by breaking the Two Lamps, could contend with most of the other Valar simultaneously, however he grew significantly weaker over time [Poured the majority of his power into Arda and his servants, leaving him drained]) | At least Universe level+ (Significantly stronger than all 14 other Valar. Second strongest being in existence. Created the concept of discord with his thoughts)
Speed: At least Supersonic+ to High Hypersonic in physical form (Far superior to the Balrogs). Possibly Infinite in spirit form (The Ainur who entered Eä were said to live at any speed of thought or motion that they chose) | Immeasurable (Transcends basic time, which the Valar did not have to abide by)
Lifting Strength: Class T+ | Immeasurable
Striking Strength: At least Multi-Solar System Class, likely Multi-Galactic | At least Universal+ (Able to beat down the other Valar)
Durability: At least Multi-Solar System level, likely Multi-Galaxy level (Able to easily fight against several other Valar, including Varda, while maintaining the upper hand, but he grew significantly weaker over time and took permanent damage from Fingolfin) | At least Universe level+ (Existed beyond the basic universe. Easily able to survive being attacked by all other Valar.)
Stamina: Extremely High | Limitless
Range: Tens of kilometers due to his size. Thousands of kilometers to planetary with magic and reality warping | Universal+
Standard Equipment: Grond, the Silmarils
Intelligence: Able to corrupt the creation of reality, was able to manipulate Ungoliant into stealing the Silmarils, corrupted half the Ainur into joining him.
Weaknesses: Has a limited amount of power that goes down the more he uses it as Morgoth | None notable
Key: Manifestation | Prime/True Form
Note: Melkor and Morgoth are both the same being. Melkor is his true name given by Eru, whereas Morgoth (meaning "the dark enemy") was given to him by his enemies. The change in name has nothing to do with anything except for where in the timeline it took place.