Star Wars Visual Dictionaries always contain a wealth of background information that is not present in the movies and The Last Jedi Visual Dictionary is proving to be a lot more helpful than most when trying to pin down details that were not addressed in Rian Johnson's first movie with the franchise. Snoke's backstory was not touched upon at all in The Last Jedi, nor was it ever going to. Johnson warned fans for months not to focus on Snoke, as he was not a big part of the story and the same can be said for Rey's parents. But some new information about Supreme Leader Snoke's origins have recently been revealed. There are major SPOILERS for The Last Jedi, so read ahead at your own risk.
It was never Rian Johnson's intent to play by the rules of Star Wars and give us a backstory about Supreme Leader Snoke and the rise of the First Order. Instead, he focused on the new main characters and let everyone else play a strong supporting role. However, The Last Jedi Visual Dictionary has provided to be a great source of filling in the blanks. We first learned of Snoke's connection to Darth Vader and Emperor Palpatine, which are based around his ring. The black obsidian stone once thought to be Kyber crystal is from underneath Vader's castle and the symbols refer to the Four Sages of Dwartii, which Palpatine studied and had statues of.
The First Order grew from the ashes of the Empire after the Battle of Jakku. From there, what was left of the Empire fled to the Unknown Regions and eventually became the First Order. The Battle of Jakku was a part of Palpatine's Contingency plan to have the Empire not go on any further after his death, but was obviously foiled when Snoke took over the reins after watching the Empire's rise to power from afar. It is now confirmed that Snoke came from the Unknown Regions and brought the First Order to power for a short time before his apprentice killed him, much like Palpatine and Darth Plagueis.
Part of the explanation of Snoke's origins in the Unknown Regions comes from a closer look on his mute attendants who were not shown in the movie. According to The Last Jedi Visual Dictionary, they had enlarged heads and wore purple robes. The books explains.
"Snoke's retinue includes mute alien navigators who originated in the Unknown Regions. Were it not for the ancient hyperspace trails blazed by these towering servants, the Imperial survivors who fled into this uncharted realm would certainly have perished. These navigators designed and operated the oculus viewing scope in Snoke's throne room."
The remaining members of the Empire were more than likely watched by Snoke and his alien navigators as they entered into the Unknown regions. These Attendants/Navigators have enlarged brains that can "process multidimensional calculations" which would be key to traversing the mostly uncharted space between the known galaxy and Unknown Regions.
This isn't the most comprehensive look at where Snoke came from, but we do know that he was collecting Galactic Empire lore, much like Luke Skywalker was doing with Jedi materials after the Battle of Endor. Snoke more than likely saw the failures of the Empire and built up from that, using much of their previous work as the backbone of the First Order. But, he didn't study Emperor Palpatine, aka Sidious,' backstory too well, learning about the cycle of apprentice killing master that is heavily prevalent in the Star Wars universe. Snoke's backstory more than likely will be explored further in some fashion, but for now, check out The Last Jedi Visual Dictionary via DK Publishing.