Stranger Things: Who Is The American?
6. Dr. Martin Brenner
Stranger Things has now established itself as a show similar to Game of Thrones in that, any character can die and nobody is safe, especially after the (presumed) deaths of Billy and Hopper. The other way it's similar is it can also follow the rule of if the actual "death" occurs offscreen, all bets are off.
Such is the case for Dr. Martin Brenner, the original big baddy daddy, who was the senior research scientist in the Hawkins National Laboratory, "raising" and testing Eleven's powers, often to torturous levels.
When Eleven and the crew escape the lab at the end of season one, Dr. Brenner is attacked by the Demogorgan, and his fate after the attack was unknown. However...
In season 2 during the, shall we say, "divisive" lost sister episode, former Department of Energy agent Ray Carroll claims to Eleven and her sister Kali that Brenner is alive and he knows his whereabouts, but we never find out where. Kamchatka, Russia perhaps?
He is obviously very knowledgeable of Eleven and her powers, and the Upside Down in general, so he would make a very valuable asset to the Russians.