: 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
The "good feature" or massive plot twist in , " The Massacre at Hawkins Lab ," is the revelation that Henry Creel (Victor Creel’s son), Number One (the first child experiment), and Vecna are all the same person. The Triple Reveal Who Is Vecna
Critics and fans often cite this episode as the best of the series due to its flawless execution of parallel storylines: Stranger Things Season 4 Episode 7 Ending Explained