First of all he was a Dark Lord of the Sith, not a Sith Lord. Secondly, we don't know who the first DLOTS was, but we know Ajunta Pall and Tulak Hord came before him. We also know he was the greatest and most powerful of the greatest and most powerful, that he was the speaker for the ancient spirits, and he had the last word on anyone vying for the title of DLOTS.