I'll preface this by saying I have no idea who Snoke is, or rather, I have no idea what his name is and it's not really that important for this theory.
Ok so a few alleged production leaks about the possible confrontation between Snoke, Kylo, Rey & Luke from the end of ep VIII got me thinking. I won't go into too much detail about the leaks, if you want to know more then you should have no problems finding details elsewhere online. Another thing that piqued my interest was a comment by JJ on the newly released 3d bluray where he says that Kylo & Rey have never met (before TFA) but that Kylo "knew of her". Yet another factor to add into my theory is that in the canon novel, Bloodline, it sets Kylo's betrayal of Luke as having taken place only six years prior to Ep VII (totally screws a fair few theories).
So I'll stop burying the lead and get to it, I think Snoke was Vader's secret apprentice and that he had been covertly creating The First Order, on Vader's instructions, as a fifth column within the Empire, the eventual goal being the overthrow of Palpatine. I think that Luke discovered evidence of Snoke's existence some time after RotJ and he tracked Snoke down with the intention of turning him or eliminating him. He meets with Snoke and actually succeeds in turning him to the light side, Snoke agrees to become Luke's padawan and together they build the new Jedi Academy. They begin to use the force to seek out other sensitives and bring them to the temple to train, even welcoming Luke's own nephew, Ben Solo, as a padawan. Now Luke has been communing with the force apparition of Obi Wan, who has been teaching him the ways of the Jedi and one of the "ways" he teaches him are the Jedi's thoughts on "attachments" (yes that stupid jedi rule is going to fuck everything up, yet again).
To cut a long story short, this comes between Luke and Snoke. Snoke falls in love with one of the other students & in secret they begin to question Master Skywalker's rigid theology. Eventually the girl falls pregnant and the two make a plan to fake the girl's death and smuggle her away from Skywalker, fearful of what they he may do if he finds out. The plan goes off without a hitch, well just the one, a pretty big one. A young Ben Solo (7 or 8), playing somewhere he shouldn't be, overhears everything. Now Ben likes Snoke & the girl (we shall just call her Rey's mother from here on out) and Snoke is able to persuade Ben to keep their secret. Rey's pregnant mother escapes unseen and Snoke (with Ben's help) is able to convince Luke that Rey's mother died in some sort of training accident.
Now before we move on to the incident six years prior to ep VII that ultimately made Luke fuck off, turned Ben & (I think) messed up Snoke, let us examine Luke & Snoke's relationship. If my theory is correct then Snoke, as Vader's apprentice, was more of a real son to Vader than Luke and Vader a father to him in return. This has to manifest as some form of jealousy in Luke. Also, Luke must have colossal daddy issues as it is, add that all up and even the wisest of Jedi might feel the pull of the dark side.
Ok, so what went down between Snoke, Luke and Kylo ? And why did Rey's mother leave her on Jakku ? Well I think as Ben grew up he essentially became the student of two masters, Snoke & Luke. Consider too that Ben has some stonking daddy issues of his own, what with Han always off adventuring & the tension that caused between him & Leia. It may be that he found in Snoke the father figure he was looking for but never got from distant Uncle Luke.
Anyway, Rey's mother has given birth to Rey and is raising her in a First Order base (Snoke's old contacts came through for him) but she begins to grow fearful that the First Order are seeking to use her daughter (who is extremely gifted in the force) as a weapon and decides to bug out. She escapes and makes it to Jakku where she decides to leave Rey, to keep her hidden from the First Order, while she leads them away.
With nowhere to turn, she decides to contact Snoke. Snoke and Ben are together when Rey's mother reaches him but as fate would have it, Luke discovers them and sees the apprentice he thought dead standing right in from of him. Enraged, he demands answers, shouting at Ben "DID YOU KNOW ABOUT THIS?! TELL ME?!" Ben is scared, he's never seen his uncle like this, he freezes and Luke, furious, rips the images from his mind. Luke knows everything. The love affair, the pregnancy, the deceit. Feeling more than a little betrayed, he draws his lightsaber on Snoke and the two throw down. Luke is a demon, he's gone man (just like at the end of Jedi) and he pummels Snoke down. Dying & desperate, Snoke blasts Luke with force lightning but Luke deflects the blast with his saber, inadvertently killing Rey's mother. That's right folks, the big ep VIII plot twist is not that Snoke is Rey's father but that Luke killed Rey's mother.
Snoke loses it, throws everything he has into a last blast of lightning, Luke, dazed, half deflects the blast back at Snoke, half catches it on his arm (that's what's up with no skin on the metal arm) and Snoke is nearly finished.
At this point it goes really mental. Ben, who has been frozen this whole time, steps forward between Luke and Snoke. "It's over Uncle Luke. The First Order are on their way, They've been tracking her". He gives Luke one chance to leave and Luke staggers to a shuttle and leaves. Just in time as First Order soldiers arrive and administer life saving treatment to Snoke.
Ben then goes to the academy & calls all the apprentices together. He explains what's happened, that Master Skywalker has betrayed them and he gives them a choice. "Join me or die". Those that resist are cut down by First Order troopers and the rest become his knights as he takes on his new name, Kylo Ren.
So we have six years of a bitter and twisted Snoke turning Kylo further & further to the dark side while Luke (after a period of moping) decides to try and discover the true secrets of the Jedi, to see if everything Obi Wan told him was true.
