Kylo Ren is a worthy apprentice to Supreme Leader Snoke but, as some have said in Star Wars, "There is another."
An official Lucasfilm magazine called The Souvenir Guide to the Movie Star Wars: The Last Jedi has a write up on Supreme Leader Snoke and, in its first paragraph, bolded and everything, is this sentence.
Force sensitive, and highly attuned to the dark side but not a Sith, Snoke has trailed Kylo Ren and at least one other apprentice
Hello! That's a very tantalising piece of information, is it not? Here's the screenshot, thanks to Slashfilm.
Now, when I first saw this via Reddit, it seemed ultra fishy. Why would this piece of information be so prominently displayed in such a seemingly random place? I still don't have an answer to that question (we've reached out to Lucasfilm for possible clarification), but this magazine is available as a download in the Star Wars Insider app, which is the official magazine of Star Wars. Plus, in the masthead, the Lucasfilm Story Group is listed.
So, that's a long way to explain that, strange as this may seem, it seems to check out as a legit piece of information.
But what does it mean? Well, the most obvious explanation is that Snoke is old. And that, sometime in his long life, he trained someone else who was strong in the Force -- and that person amounted to nothing or died. That's the most likely scenario. The favourite, if we were taking odds. He obviously had a history before we met him in The Force Awakens and it would make sense that Kylo Ren wasn't his first apprentice as he rose to prominence in the First Order
But speculation is always fun. Could there be another apprentice lurking somewhere? A person Snoke cast to the side when he realised how strong Ben Solo is? Someone who is now off in the Outer Rim and really, really pissed off? Or are the Knights of Ren just considered apprentices as well?
There are a bunch of different possibilities, none of which are accurate until a story is told about one. But it feels like no matter what the answer, the fact this piece of information was specifically called out means there probably is one. Or will be.