- "Always two, there are; no more, no less. A master and an apprentice."
Dark Lord of the Sith was a title shared by Sith Lords who were members of the ancient Sith Order. A thousand years before the rise of the Galactic Empire, the Sith had all but destroyed one another due to infighting and constant war with the Jedi. In the aftermath of their destruction, Darth Bane, sole survivor of the Sith's destruction, assumed the title and established a philosophy known as the Rule of Two, saying that only two dark lords could exist at any given time.
By the time of the Galactic Republic, the Dark Lords of the Sith adhered to Bane's teachings. Sheev Palpatine, also known as Darth Sidious, was the reigning Dark Lord of the Sith during the era of the Galactic Empire. Darth Vader also assumed the mantle after becoming Sidious's Sith apprentice.