Supreme Leader Snoke is a fictional male in the Star Wars series. The character was portrayed on screen by Andy Serkis. His allegiance / loyalty is to The First Order. Supreme Leader Snoke is played by Andy Serkis, the man who directors and producers turn to when they want someone to do stop motion acting. Details on the character have not been revealed as yet. Lets just hope, its better than the previous human-CGI character, Jar Jar Binks.
Supreme Leader Snoke is the leader of First Order, the remnants of Emperor Palpatine's organisation, the Galactic Empire to whom both General Hux and Kylo Ren answer to. As he is C.G.I, they're holding this one very close to their chests so it is a surprise for everyone when they see him. They're also doing the same to Luke Skywalker by showing very little of him. Snoke is very much interested in Luke Skywalker, maybe they think they can turn him to the dark side of the force where others have failed.
Supreme Leader Snoke only appears as a hologram when he gives instruction to General Hux and Kylo Ren on how best to proceed. He appears as a giant but as its a hologram, its not able to ascertain exactly how big the character is supposed to be. Like the Emperor in star Wars V - The Empire Strikes Back, Snoke only appeared as a hologram. Some had theorized that Snoke could be a son of Han Solo or Luke Skywalker but both theories are wrong. The theory that Snoke is the son of Han Solo went sideways when it was revealed Han has only got one child and that's Ben Solo who went onto become Kylo Ren. His character is guaranteed to be back for the next films in the series, the next due out in May 2017.
The producers toyed with the idea of making Snoke a female who had extra-ordinary beauty. However they decided instead to go for a C.G.I. character instead, a non-human by the looks of him in the film. There is a rumour going round that implies that Snoke could be Darth Plagueis the wise. According to Palpatine in Star Wars III - Revenge of the Sith, Plagueis was so obsessed with life and death and had worked a way to bring people back to life again, he could have bought himself back to life first as a force ghost then as a real person.
Supreme Leader Snoke is most likely a Sith Lord as he tells General Hux that both he and Kylo Ren should come to him so that Kylo's training be completed. Its not clear as to whether Snoke will carry out the training himself or someone else will do it.
Snoke's past is not revealed in the films, in the second film, when the Resistance escape from D'Qar, Snoke insists on General Hux reporting back to him, explaining what went wrong. A giant holographic picture of Snoke appears on the bridge of Hux's Star Destroyer. When we finally see Snoke, he's in a room guarded by Red Imperial Guard like people. Snoke is disfigured like in his hologram. Snoke is only marginally bigger than Kylo Ren, we're talking inches.
Snoke had a personal interest in Ben Solo and managed to corrupt Ben before Ben became Kylo Ren. Ben turning to the dark side scared Luke Skywalker who attempted to kill Ben but Ben woke up and prevented Luke from carrying out the execution. In the ensuing battle, Kylo Ren destroyed all that was left of the Jedi order and Luke's Temple.
Snoke describes seeing Ben as someone who had raw untapped potential, something that Snoke wanted to tap into. Kylo Ren was able to lure Rey to Snoke star destroyer and introduce him to her. When Kylo Ren refused to behead Rey for not wanting to join the First Order, Kylo turned on Snoke and killed him by activating the lightsaber that was positioned next to Snoke.
With Snoke now dead, both Kylo Ren and General Hux vied for the position of the new supreme leader. Kylo Ren force strangled General Hux into submission and became the new Supreme Leader. Its unlikely we will learn how Snoke gained control of the First Order, the remnants of the Galactic Empire in the film canon. We may learn in the spin-off books on how Snoke gained so much power.