That he does it all with schoolboy glee makes him that much more viscerally loathsome — Mr. Rheon conceived Ramsay as a mash-up of Heath Ledger’s unhinged Joker and Dennis the Menace, he said, and added a bit of the swagger of Liam Gallagher, the dyspeptic former Oasis singer. The resulting confection has landed on many “most-hated” lists online. In December, readers of The Atlantic voted Ramsay “the actual worst character on television” over the likes of Hannibal Lecter and Walter White, as well as Joffrey Baratheon, the sneering boy-king Ramsay replaced as the signature “Game of Thrones” villain.

“After we lost Joffrey, we had a psychopath-shaped hole in the ‘Thrones’ world,” Ms. Turner wrote in an email. “But Iwan brings a terror and a creepiness that Joffrey never had. We needed someone to hate, and we love to hate him.”

In the new season, the show’s sixth, Ramsay deepens further, Mr. Rheon suggested, even approaching something like human emotion in mourning a girlfriend killed in the Season 5 finale. “That surprised even me,” he said. Of course, it also finds him seething over last season’s escape of his captives Sansa and Theon (Alfie Allen) — the young nobleman he castrated, forced into servitude and renamed Reek — and sets up who may be his most appalling victim yet: an as-yet-unborn half-sibling who could be a competing heir.

[ “Game of Thrones” has moved past its blueprint. That’s a good thing. ]

The show’s creators, David Benioff and D. B. Weiss, so obsessed with secrecy this season they’ve declined to offer critics advance screener copies, will say only that Ramsay will be up to “very bad things.”

“Sometimes you just think, ‘Oh God, can’t we just do something nice?’” Mr. Rheon said, laughing. “On this show, the heroes aren’t necessarily standard heroes, so I guess your villains need to be even worse.”