Dark Lord

Dark Lord was the title of the two most powerful evil overlords in the world of Arda, the first of whom tried to destroy Arda and the second to control it and enslave it's inhabitants.

Description
That which they could not control, they sought to destroy. The first Dark Lord was the Vala first known as Melkor and then as Morgoth. The second Dark Lord was the Maia, and former servant of Aule the Vala and chief lieutenant to Morgoth known as Sauron. Both Dark Lords were very influential in the history of Middle-earth, waging numerous wars against the Valar, the Elves, and a few select groups of Men. Their actions, especially those of Sauron, had a permanent negative impact on the world, for both of them destroyed many beautiful things and places, and caused untold anguish and grief. However, Sauron is recognized as the greater of the two, due to his manipulation and ambitions (he is called Dark Lord more than Morgoth is). Eventually both Dark Lords were overthrown and defeated; Melkor was cast into the Void at the end of the First Age by his brethren, and Sauron was permanently defeated at the end of the Third Age by Frodo Baggins with the aid of Samwise Gamgee and Gollum, when they cast the One Ring into Mount Doom and robbed Sauron of most of his power.

Dark Lords:

 * Melkor, later known as Morgoth, the Dark Lord of the First Age
 * Sauron, the Dark Lord of the Second and Third Age