: Eleven's "mentor" in the lab is revealed to be 001 , the powerful first subject of Dr. Brenner's experiments.
: 001 is actually the young Henry Creel , who was not killed by his father but was taken by Brenner after murdering his own mother and sister. [S4E7] Plot Twist
Who Is Vecna? The final moments of Stranger Things season 4 episode 7 reveal that Henry Creel a.k.a. Number One is the monster we' Den of Geek Chapter Seven: The Massacre at Hawkins Lab - IMDb : Eleven's "mentor" in the lab is revealed
: Eleven defeats 001 by pushing him through a portal into the Upside Down , where the dimension’s environment transforms him into the monstrous Vecna . Why It Is Highly Rated [S4E7] Plot Twist