A new Star Wars: The Rise of Skywalker theory states Emperor Palpatine has been behind Snoke the entire time. Star Wars fans have been wondering about a possible connection between the mysterious Supreme Leader Snoke and Palpatine for years now, but The Last Jedi brought more questions to the surface. There are certain elements that connect the two villains, which are official canon. One of those connections is Snoke's ring made of Kyber crystal, featuring The Four Sages of Dwartii. Palpatine had the actual Sages of Dwartii statues in his office, which Snoke later obtains.
The Rise of Skywalker fan theory states that Emperor Palpatine has been behind Snoke since the start. "The spirit of Sidious haunted Snoke his whole life," according to the theory, which goes on to state that Palpatine believed Snoke could do what he was not able to do. Additionally, the theory draws parallels between Palpatine's fate and Snoke's since they both get overthrown by allies. This would certainly go a long way in explaining how Palpatine is back in The Rise of Skywalker.
The Last Jedi novelization shed some more light on Snoke's mysterious past. Snoke was the unexpected leader of the First Order, meaning nobody really saw him coming. The last of the Imperial leadership, including Gallius Rax, Sloane, the political lunatic Ormes Apolin, or even Brendol Hux did not see Snoke's rise to power and were shocked when it occurred. Snoke arranged to have them killed except for Hux, who he used as a tool. His rise within the First Order was not by plan, but was instead more opportunistic, according to the book. This is where things start to get a little interesting.
The Last Jedi novelization claims that Emperor Palpatine knew of Snoke, but did not know he would go on to take over the First Order. Snoke knew all about Palpatine's contingency plan, Operation Cinder, which was engineered to destroy the Empire in order to rebuild, but much stronger this time around. Since we know that Palpatine was aware of Snoke before his death, it is certainly possible he could have gotten into using him as a puppet in the afterlife. It should be noted that the novel does state that Palpatine could not sense what Snoke was up to.
Snoke saved the First Order from many attacks and brought it to the strength that it is at today. This certainly sounds like the contingency plan Emperor Palpatine had in mind the entire time, so why shouldn't he ultimately be the one behind it? J.J. Abrams has a lot of explaining to do in The Rise of Skywalker and fans are hoping we'll get some more information on Snoke in the process. It seems Snoke and Palpatine have to be connected in more ways than what we just talked about. We'll just have to wait and see. Until then, you can check out the fan theory over at Reddit.