William

William turns up in a prison interview room as one more subject in the Bureau's ongoing study of violent offenders. He answers Holden Ford and Bill Tench's questions with the wary, measuring calm of a man used to being watched, giving them just enough to keep the conversation going.

Mindhunter's power comes from these procedural encounters, and Evander Duck Jr. plays William with the show's signature restraint — no menace performed for the camera, just a flat, controlled voice that makes the agents, and the audience, lean in to catch what isn't being said outright.