In the official release of the first stills of Supreme Leader Snoke (Andy Serkis) and Maz Kanata ( Lupita Nyong’o) Entertainment Weekly confirmed that Snoke is " … just Snoke." In other words, he's not Darth Plagueis, the Sith Lord and master of Darth Sidious (who in turn, was the master of Kylo Ren's grandfather, Darth Vader). From previous quotes from Serkis, we learn that Snoke is a Sith Lord who is suffering from severe physical damage, which might explain his absence from the Original Trilogy and prequels. It's quite apparent that he's been in a serious fight as evidenced by his heavily scarred face. The question then becomes, was it damage from Jedi warriors or other Sith Lords?