It's somewhat possible that 'Snoke' is an alternate persona of Lukes; an illusion he puts forward when acting as the dark lord.
Wild, crazy theory: In the Empire Strikes Back, when Yoda warned Luke that if he left for Cloud City before his training was complete he would be lost to the dark side, he meant it. While succeeding in keeping his cool and turning Vader back to the light, his father's death and the torment inflicted on him by the Emperor took its tole, and in the years to follow, while he tried to rebuild the Jedi order, love of a woman led him astray. They had a child in secret, and Luke became obsessed with its protection, the jaded past of the woman he loved become a killing field as it came back to haunt her. Realizing what Luke was becoming, she fled with the child, hiding it on a remote world and then leaving to spread false trails across the galaxy. Luke, realizing all the powers of the Jedi could never lead him to his child, concocts/is overcome by the persona of Snope, twisting the mind of his young Padawan Ben Solo to serve his purpose, the newly named Kylo Ren wholly unaware that his former Jedi Master and newfound Sith Lord are one in the same. Together they infiltrate a powerful sect of the fractured and leaderless Empire, who happily fall in line with the traditional Sith hierarchy, and begin rallying/rebuilding in the form of The First Order, an organization capable of scouring the Galaxy. The Republic, realizing the First Order is becoming a threat but not wanting the Star Wars to begin again, enters into a treaty agreeing no support will be given to rebel/resistance elements so long as the First Order ceased all aggressive actions against the Republic. Snope is adamant however, and with years of searching failing to yield results, decides the only way to find his daughter is to lure her to him. Knowing full well how the Force works and the cyclical nature of his reality, he does what he needs to do to draw out the destiny of a latent New Hope; he builds a death-machine the likes of which the Force simply can't tolerate. Thus, the destiny of the daughter of Skywalker 'awakens', and puts her on a path of inevitable confrontation with her father, whether that be presented to Snope by Kylo Ren, or standing before Skywalker of her own volition. When Kylo is defeated, and Rey returns to the Rebel Base, R2D2 abruptly rouses from his long slumber, and gives her the map straight to Luke's doorstep.