Third Dark Lord, or Melkor's Return?

[Inziladun]

Originally Posted by Mithadan

Assuming that the Prophecy remains part of the mythos, Morgoth would return in his own body. Some earlier writings had Morgoth being executed following his capture after the fall of Angband. Tolkien rejected this idea for a few reasons. First, he felt that it was not in the nature of the Valar to execute him. Second, Morgoth's death was inconsistent with his later conception of the Valar as perpetual and not able to be "slain." They can be weakened to the point where they cannot construct a physical body, but their spirit would remain. The final iteration was that Morgoth was physically bound with Angainor and expelled into the void. So he had a body for what it's worth.

This is fairly in line with Christianity also, in which the Book of Revelation tells of a period when Satan will be released from Hell and allowed to return, after being bound.

And when the thousand years are expired, Satan shall be loosed out of his prison. And shall go out to deceive the nations which are in the four corners of the earth, Gog and Magog, to gather them together to battle: the number of whom is as the sand of the sea.

Rev 20:7,8 KJV

I wonder if Tolkien's ideas there were colored by Revelation.
Satan is to be defeated by direct intervention from God, though as Mithadan notes the Second Prophesy may have had Túrin being the destroyer of Morgoth.
It would have been nice to see Túrin getting the chance to repay his tormentor, and save Arda in the bargain.