The Sith have long been mystical and fan-favorite characters throughout Star Wars' 43-year history. The Expanded Universe had multiple stories diving into the Sith and their history, including the Tales of the Jedi comic series, the Darth Bane trilogy of novels, and the Darth Plagueis novel. The current canon hasn't really delved much into the history of the Sith, but Disney Plus has a chance to change that.
Source：https://www.cbr.com/star-wars-tales-of-the-sith-show/
