There is content here pertaining to the endings or Star Wars: The Old Republic, Knights of the Old Republic and stuff about the expanded universe. Be warned, there are spoilers.
Following the lore of Star Wars, including the expanded universe, I decided to do a lot of digging in order to locate any information on possible Sith. And wow, did I find out a lot of information.
In the lore, Revan, in between KOTOR and SW:TOR decided to venture out into the unknown regions, in order to locate the hidden Sith threat, which I believe is the 'true' Sith, a race of hyper-advanced Sith lords lving in uncharted space, seeking retribution for the deeds surrounding Exar Kun.
Now, for those of you who don't know already, Revan made contact with the 'true' Sith, a.k.a the Red Sith, and managed to resist complete control through powerful mind domination, but his best friend and apprentice Malak wasn't successful. Revan returned to the galaxy with the intent to strengthen it, through a fake war, while eliminating key targets preventing this ideal, and hoping to prepare it for the invasion of the Red Sith through the power of the Star Forge. Unfortunately, this goes pear-shaped and Revan is forced to kill Malak after having his mind wiped by the Jedi, spelunking numerous planets for star maps, and destroying the Star Forge.
Revan, after regaining his knowledge on the Red Sith, scouts the unknown regions attempting to find out how many Red Sith he had to fight, leaving his wife, Bastila Shan, and their child alone. Revan proceeded to be captured and tortured, with his very force energy being drained (which isn't THAT bad for him - he DOES have unlimited light and dark side force) as well as, apparently, his soul. After the awful storyline that is Star Wars, The Old Republic, which I shall NOT be discussing here, he is apparently 'dead' (I am not happy) and the events of the Star Wars saga continue.
Now, I could mention the fact that Kylo Ren's mask and robes seem styled after Revan, but I'm not going to speculate that possibly he found Revan's holocrons detailing his Sith powers and thought, "Revan is obviously a Sith Lord I must follow his evilness to the 'T' hahahaha!" and write an article about it. What I do think, however, is that it is possible that Kylo Ren found Revan's holocrons, and somehow acquired information on the Red Sith. Either this, or he just plain got abducted by the Red Sith and was trained by them. Anyway, I believe his masters are the Red Sith, and the fact that both the 'light' and 'dark' sides of the force awakening is mentioning how there's always a balance in the force - when the 'light' gets stronger, so does the 'dark'. This is, of course, meaning that those using the dark would get stronger, not talking about the fact that people assume 'light'=good and 'dark'=bad or any of that bull.
Anyway, if you've read past this insane rambling long enough thank you for reading, and it would be nice to see any responses given, if you have the time and or commitment.