Photographs By Nino Munoz

Preparing to play a suburban schlub in HBO’s “DTF St. Louis,” David Harbour decided he needed to transform — slightly.

“I guess it’s just part of my process,” he recalls, “because when I looked at it, it wasn’t that much bigger than myself.” He’s referring to the prosthetic belly the production designed so that Harbour, as ASL interpreter Floyd Smernitch, could believably be Midwestern-dad pudgy. Harbour is hardly willowy — on “Stranger Things,” where he played heroic small-town police chief Jim Hopper for five seasons, his weight fluctuated, and sitting before me, he cuts an imposing figure. But Floyd carries himself with a certain dejection, and the belly helped.

“It’s a little bit about the landscape of America,” Harbour says. He has just seen the new revival of “Death of a Salesman,” and recalls that Lee J. Cobb, who originated the role of Willy Loman in 1949, helped to shape the role around his large frame — his Willy complained that he was an unsuccessful salesman because of his weight. “I’m always thinking of the archetype of the American man and the American dream.”

Perhaps the point was allowing Harbour, now 51, to feel different from himself. “I don’t know that it was extremely necessary, but it helped me put on a bit of a mask. I think the facial hair does too — it allows me to liberate the true soul beneath,” Harbour says. (As we sit on the patio of an East Village coffee shop near Harbour’s Manhattan home, the actor is affably scruffy in sweatpants and beat-up sneakers.) “I don’t think I could have danced as fun and as free as I did without that belly.”