General Grievous isn’t a Sith Lord, although he shares plenty in common with those who are. He loathes the Jedi. He’s a proficient lightsaber duellist trained (as he’s fond of pointing out) by Sith ...
General Grievous has a noticeable cough in Star Wars: Episode III – Revenge of the Sith, and, naturally, the Star Wars franchise’s non-movie materials explain the origin of this curious detail.