“Succession,” one of the year’s surprise breakout hits, initially attracted a cult following.

But with the show’s second season, it became the thing everyone was talking about — and not just in the media, where shows about media-based backstabbers exert a sick fascination.

The Jesse Armstrong drama, whose season finale airs Sunday at 9 p.m. on HBO, concerns how mogul Logan Roy (Brian Cox), like King Lear, will divide up his kingdom, Waystar Royco. His conniving children — Kendall (Jeremy Strong), Shiv (Sarah Snook) and Roman (Kieran Culkin) — lie in wait, eager to please, ready to pounce, while Logan plays head games with them.

Cox thinks he knows why this particular corrupt family has captured the public.

“The show’s a morality tale,” says Cox, 73. “It reflects our fixation on wealth and success and how hollow they are.”

Two burning questions lay at the heart of “Succession.” Which real-life mogul was the inspiration for Logan? Cox insists he is Armstrong’s creation. “He’s not like [Rupert] Murdoch, he’s not like Trump,” Cox says. “He didn’t inherit money.”

The second question: Why doesn’t Logan trust his children to take over the company?

“It’s complicated,” he says. “Logan’s trying to find the kid who has what is required. Shiv’s problem is she talks too much, gives it all away. He really loves her and thinks she has the potential.

“Kendall is f—ed. He’s in a very frail state, trying to reinvent himself. Logan is fiercely protective of him because he sometimes lacks gumption. He’s not sure of the boy’s capacity to really be a killer.”

Roman, the youngest Roy, may be Logan’s best bet. “Logan calls him a f–k-knuckle, but Roman is actually much smarter than he originally thought,” he says. “And Logan starts putting him in more responsible situations.”

Not that the old man, whom Cox terms “a mystery wrapped up in an enigma,” is easy to read — or reach. Does he love his kids? “Yes,” Cox says. “He loves them so much. He’s also so aware of their shortcomings.”

The Scottish-born actor describes the season finale of “Succession” as a “doozy,” down to the last frame. Until Season 3 premieres next year, you can catch him playing another, real-life powerful man — LBJ — in the play “The Great Society,” now at Lincoln Center’s Vivian Beaumont Theater. Johnson — whose civil rights reforms were overshadowed by America’s deepening involvement in the Vietnam War — emerges as a more sympathetic figure than you’d expect. “He was flawed but there was a virtue at the center of his life,” Cox says.

After you’ve seen Logan invent a twisted game called Boar on the Floor, where his male executives are made to crawl on the floor and oink like pigs, you will think LBJ is an angel.

“We actually saw the true demon that is Logan,” Cox says.

With his commanding voice, Cox, who lives in downtown Brooklyn, is more in demand than ever. He chalks up his success to his education at the London Academy of Music and Dramatic Art.

“I did well when I was young actor. I was reasonably successful,” he says. “But it’s gotten so much busier. So many of my contemporaries are falling off the perch. Actors go on until we drop because of our artistic imperatives and the challenge of a new guy: Churchill. Logan. And doing LBJ . . . It’s a tough gift because you have to deliver.”