What is the Dark Lord's real name?

Answer 1

Depends on which Dark Lord you are talking about. The first Dark Lord, of whom "Sauron of Mordor was only a servant," was Morgoth, formerly Melkor, a fallen Power/god. The second Dark Lord, was as you probably figured out, Sauron, also known as Gorthaur the Cruel. He was the "right-hand man" of Morgoth, and was a lesser spirit of power. See related links for more.