«The Darth title was more than just a symbol of power; it was a claim of supremacy. It was used by those Dark Lords who have sought to enforce their will on the other Masters. It was a challenge — a warning to bow down or be destroyed.»
“It was no accident that I took the title of Darth. Nor was it an accident that Ka’an and his ilk rejected it” Darth Bane: book of sith