The British actor appears as a grotesque supernatural villain in the hit Netflix show as well as one of the wardens at the laboratory where Eleven is kept.
In order to get into the mindset of such a creature, the 33-year-old revealed he would print off photos of his victims and cross out their eyes.
“I would take photographs of each victim,” Bower told People. “I’d print them off, my next victim, and I would cross their eyes out and put them up on my wall. And I’d stare at them.”
The actor explained that resentment was a “massive driving force for Vecna”; “And so preparing was about bringing that up and digging that up more, [which meant] a lot of heavy, dark meditation, low-frequency sounds, a lot of saying the same kind of thing over and over again.
"I would clear my mind and then have these phrases that I would just put in over and over and over again. Walking around late at night. Isolation on my own was always a good thing."
It also helped Bower that he was in heavy prosthetics while playing the demonic character. The show’s make-up designer Barrie Gower told RadioTimes.com recently that Bower spent an average of about seven hours in make-up transforming into the villain.
Bower revealed that he left co-star Millie Bobby Brown “in tears” because he was “so scary” on set, in character as the young Henry Creel.
Meanwhile, the show’s creators, the Duffer Brothers, have responded to Millie Bobby Brown’s criticism of their failure to kill many characters off.
You can read The Independent’s five-star review of Stranger Things season four, part two here.