Title of Darth

Darth was a title given to the Dark Lords of the Sith Order, which preceded a moniker different from the birth name. The Sith names of the Dark Lords, and  were Darth Sidious, Darth Tyranus, Darth Vader and Darth Bane, respectively.

The title was already in use about one millennium before the Clone Wars, when Darth Bane created the Rule of Two. In at least two known cases, that of Dooku and Anakin Skywalker, the Darth title were bestowed onto the Sith Apprentice by the Sith Master.

The once used "Darth" as a form of address when talking to Darth Vader. It was traditional that only the current Sith Master and his or her apprentice were allowed to use the Darth title. Imperial officers typically addressed Vader as " Lord Vader".