In Star Wars: Attack of the Clones and Revenge of the Sith, Christopher Lee suited up as the villainous Count Dooku, who played a pivotal role in Anakin Skywalker's fall to the dark side. While Dooku was certainly evil -- and even had a Darth sobriquet, Tyranus, that he rarely used -- he was never quite a Sith, at least not in the true sense. Unlike those who espoused the Sith doctrine, Dooku wasn't motivated by hatred or fear, but by the same purpose that drove him as a Jedi. Dooku even tried to spare Obi-Wan Kenobi on two occasions, and bring him to his cause.
Source：https://www.cbr.com/star-wars-count-dooku-never-sith-tried-save-obi-wan/
