For McCallany — whose screen credits include “Nightmare Alley,” “Three Kings,” and “Fight Club,” in addition to his lead role on “Mindhunter” — the key to playing Fritz Von Erich, who was not just a three-time world champion but one of the most feared heels of his day, was learning not just how to wrestle, but how to do it in the actual style of Von Erich himself.

“Different wrestlers have different styles, different identities,” McCallany says. “Fritz was a big, strong guy, and in the wrestling game, they call a guy like that stiff, which means that he’s not there necessarily to take it easy on you. In fact, there were certain wrestlers in his era that didn’t want to wrestle Fritz Von Erich, because they said, ‘No, I’m just going to get injured.’ You know what I mean? ‘He’s too tough, he’s rough in there. Don’t bring me Fritz.'”

The result of McCallany efforts is an outstanding performance in “The Iron Claw” as a wrestler and businessman who was often merciless as a fighter, and who carried that ruthlessness into both his leadership of World Class Championship Wrestling and the raising of his six sons, five of whom preceded him in death even as most of them also followed him into the ring.

“That’s where the journey began for me,” McCallany concludes. “Just doing enough training and learning enough about the sport so that I could feel within myself that I had earned the right to walk out there in front of the cameras and play a professional wrestler, and specifically play Fritz Von Erich.”

“The Iron Claw” is out now in theaters.