In The Rise of Skywalker, we see that
Darth Sidious is not only still alive, but has built a laboratory that includes tanks with Snoke-clones gestating inside. Sidious claims to Kylo Ren that he "made" Snoke.
Snoke's role in the sequel trilogy seems to be to turn Ren to the Dark side and train him as a Sith, even getting himself killed by his apprentice like in the old Sith tradition. Could this be because he is simply a puppet controlled by
If he wasn't a puppet, but rather an individual with free will, why wasn't he a Sith serving his master? He was way more powerful than either Ren or Rey at the time of his death, and had no second thoughts about the Dark side. It seems that he would have been a very useful ally to his master. Instead, he was disposed of, and his master didn't seem overly bothered by his demise.