Snoke was introduced in Star Wars: The Force Awakens as the supreme leader of the First Order and Kylo Ren's master. But his main purpose in that movie was delivering commands from afar via hologram, and we didn't learn anything else about this mysterious humanoid other than he has a connection to The Force. Snoke will receive significantly more screen time this winter in Star Wars: The Last Jedi, but his increased presence doesn't mean we'll learn a whole lot about his background. As director Rian Johnson put it:
Similar to Rey's parentage, Snoke is here to serve a function in the story. And a story is not a Wikipedia page. For example, in the original trilogy, we didn't know anything about the Emperor except what Luke knew about him, that he's the evil guy behind Vader. Then in the prequels, you knew everything about Palpatine because his rise to power was the story. [In The Last Jedi], we'll learn exactly as much about Snoke as we need to.
Although The Last Jedi will expand upon Snoke's overall character and his goals, Rian Johnson provided the above answer to EW regarding whether or not the next Star Wars movie will provide all the answers about Snoke's past. He then added that "we'll learn exactly as much about Snoke as we need to." Despite the lack of forthcoming actors, Johnson assured fans that Andy Serkis will have a lot more to do in The Last Jedi, as well as noted that contrary to a report claiming that Snoke would be a puppet this time around, the First Order's leader will remain a motion-capture creation.
There were two important mysteries established in The Force Awakens: where Rey came from and who exactly Snoke is. While The Last Jedi is expected to provide a substantial about of information about Rey (though not necessarily everything), it sounds like fans will have to wait until 2019's Episode IX to learn about Snoke's background. Even then, what's to say we'll get the full story on him? This may end up being another Palpatine situation where are still select questions left unanswered when this trilogy concludes. Ideally Episode IX won't disappoint with shedding light on this deformed antagonist, and if there's still a fair amount of backstory left to be revealed afterwards, then the gaps can be filled in a book, comic book series or TV show.
As for The Last Jedi, it doesn't sound like Snoke will be lacking in opportunities to shine. We'll finally see him together with Kylo Ren, and although Snoke is protected by the elite Praetorian Guard, that doesn't mean he might not show off his special abilities. Snoke may look frail, but appearances can be deceiving, especially with those who can harness The Force.
We'll find out what plans and schemes Snoke has cooking when Star Wars: The Last Jedi is released on December 15.