Season 4 of Stranger Things sheds light on hitherto unknown details about Eleven's complicated past. Take the Season 4 opener, which features a bloodied massacre at the lab where El was trained.

The segment kicks off with an exploration of Dr. Martin Brenner's (Matthew Modine) neatly-choreographed morning routine, which is followed by a few frames showing the experiments he is busy conducting with a kid well-versed in telepathy. Jump cut to: Eleven standing in the blood-covered Rainbow Room of the Hawkins National Laboratory, surrounded by dead bodies.

As Season 4, Episode 1 seems to imply, El could have easily been the kid behind the ghastly deed. However, as Season 4, Episode 7 reveals, that's not quite how the tragedy panned out.

The latest episodes introduce viewers to a new antagonist — One, aka Vecna) (Jamie Campbell Bower). One telepathically massacres his mother and sister and allows his father, Victor Creel (Robert Englund), to take the blame for his crimes.

He is then admitted to the Hawkins National Laboratory, where he becomes the first child to undergo Brenner's experiments. Things take a very dark turn once One decides that it's time to emanate himself from the shackles. Of course, if you've watched the whole first part of Season 4, you know that One ends up murdering everyone at the lab. Subsequently, Eleven banishes him to the Upside-Down, where he then becomes Vecna.