There has been more speculation about Snoke’s identity than pretty much anything else in The Force Awakens.

Is he alive (and shown as a hologram), or dead (i.e. a spirit/”space ghost” like Yoda and Obi-Wan)?  Is he Vader? The Emperor?  Obviously, he is not Porkins.

Andy Serkis was quoted as saying that Snoke is a new character, so maybe any and all speculation is pointless.   Still, my favorite theory is that Snoke is the “dead” Darth Plagueis, re-appearing as a “space ghost”.