Snoke is revealed to be the master maniupulator and schemer from the very beginning. He has been pulling the strings from the very beginning since before the prequels until now. He is Darth Plagueis.
Darth Plagueis is dead
Even if he wasn't, word of god is no Sith appear in the ST.
He let the emporer do his work for him until the time was right and the empire fell. Then he could take control of the remnants when they were at their weakest and needed a new leader. Then the galaxy would be at their most vulnerable because they have just won. Nobody would suspect him.
But... the First Order is a shittier version of the Empire, he's objectively working with less than he could have
It is then revealed in a conversation between rey and luke (as a force ghost) that he knows who her parents are. But they were not junk traders. He could tell from he force that awakened within her.
She is plageuis's daughter.
That's honestly stupid