If there is a word most used to describe Jim Hopper (David Harbour) on “Stranger Things,” odds are high that it’s “dad.”

Harbour agrees. Ahead of “Stranger Things 4: Volume 2,” the actor spoke to IndieWire from London, where he’s starring in “Mad House” with Bill Pullman. Like Hopper in “Volume 1,” the actor is largely removed from his castmates as the Upside Down descends again on Hawkins, In., but he reflected to IndieWire on the years spent playing this character and its inextricable link to his own life.

“I was just ‘dad’ to a lot of people!” he said, noting his history as a “wacky artist” and single man. “It was a very surprising thing, and it allowed me to open the door to wanting that. Now I have that in my own life as well.”

Harbour’s fatherly journey took off with Hopper, a grieving man whose quest...