The latest Star Wars novel hints that Palpatine could have been training Count Dooku years before Darth Maul died in Star Wars: Episode I - The Phantom Menace. For centuries, the Jedi had believed the Sith to be extinct - right up until Darth Maul engaged Qui-Gon Jinn on Tatooine, and then was killed on Naboo.
The Jedi knew that, ever since the time of Darth Bane, the Sith had operated under the Rule of Two. This mandated that there could only be two Sith at any one time; one Master and one Apprentice, one to crave power and the other to wield it. They believed that Darth Maul was the apprentice, which logically meant that the Sith Lord would be seeking out a replacement - and he found Count Dooku, a former Jedi Master.
Of course, though the Jedi didn't know it, the Sith Lord was actually Palpatine, who rejoiced in the Sith name of Darth Sidious. But Claudia Gray's latest novel, Master and Apprentice, raises the disturbing possibility that Sidious hadn't been going by the Rule of Two at all, and that he may have secretly been training Dooku before the prequels even began. The book is set seven years before the events of The Phantom Menace, and it reveals that Dooku had left the Jedi Order years before the Sith made themselves known. What's more, in one key scene he has a conversation with his old apprentice, Rael Aveross, and it's clear Dooku has already fallen to the dark side.
"You would learn much here on Serenno with me. You have yet to even imagine the truth of the Force, but you could find the way. There are so many things I've learned, that I could teach you - far more than they ever told us at the Temple. You will gain more understanding, more power, than you can yet comprehend. If we stood together - we would be unconquerable."
Master and Apprentice suggests that Dooku had always been interested in the dark side of the Force; one flashback scene seems to show him knowing how to summon Force Lightning years before he defected from the Jedi. But these comments seem to go beyond the dark side and lean heavily into the ways of the Sith. The only question is whether Count Dooku was researching the Sith independently - or whether he had already been approached, and was being mentored, by Darth Sidious. Certainly Dooku appears to be following the same modus operandii he would take during the Clone Wars, undermining the Jedi and attempting to persuade other Force-users to learn under his tutelage. What's more, it makes sense that he'd reach out to Rael first; his first apprentice, Rael had never been particularly wary of the dark side, and he'd suffered a personal blow that potentially made him easy to manipulate.
If Count Dooku was already working for Sidious, then it suggests Palpatine cared little for the ways of the Sith; seven years before Star Wars: The Phantom Menace, he was already breaking the Rule of Two. It's certainly in character; after he became the Emperor, Palpatine had no problem using other Force sensitives and - according to tie-in comics - even considering replacing Darth Vader with apprentices who simulated Force powers using technology. Vader considered several of Palpatine's decisions to be outright heresy, so it wouldn't be a surprise to see the Dark Lord departing from the Sith traditions at an earlier stage.
But if Palpatine was actually training two Sith apprentices at once - was he training more? It's entirely possible Palpatine trained other dark side users in the ways of the Sith, that there are other apprentices out there, as yet unseen in Star Wars canon. Given the Emperor is set to return in Star Wars: The Rise of Skywalker, this may well prove to be important. It's even possible that Supreme Leader Snoke, a powerful dark sider, was trained by Palpatine.
