First, let us consider the question of Sumner Redstone’s delicate health. He is 91 and clearly ailing. But he has been living for years with physical disability, ever since he was terribly burned in a March 1979 fire at Boston’s Copley Plaza hotel. Redstone survived only by hanging onto a third-story windowsill as his right hand burned, until he was rescued by a ladder from a fire truck on the ground below. He endured five operations, more than 60 hours of surgery, to repair the damage, which included burns over 45 percent of his body. The incident left his arms and legs scarred and his right hand a gnarled hook. It took him a full year to recover. Every time his bandages were removed, he was pumped full of morphine. That he survived, and thrived, is a testament to “sheer will,” Hollywood studio executive Dennis Stanfill once said. Explained Redstone in 1989, “I only think about it when I’m hitting a tennis ball and say how damn lucky I am.” (The tennis racket is strapped to his right hand to allow him to play.)

For years, he has taken to professing, simply, that he will live forever. In April 2009 he told Larry King at an overflow audience at the Milken Institute, in Santa Monica, “The people who fear dying are people who are going to die. I’m not going to die.”

But Redstone was just warming up. He told King he worked out 50 minutes every day, without fail, usually by swimming in the nude in one of the pools on his sprawling estate, in the Beverly Park section of Los Angeles. He is careful about what he eats. “I eat and drink every antioxidant known to man,” he said. That includes “goji berries, Green Machine smoothies, and tomato juice.”

And then there was the sex. “I feel better than I did when I was 20,” he continued, “in every facet,” even sexually.

Almost five years later, he still believed he was immortal. Asked in his last public interview, in January 2014, with The Hollywood Reporter, about who might succeed him, he exploded, “I will not discuss succession. You know why? I’m not going to die.”

But Redstone’s immortality, or lack of it, is of immense importance to Philippe Dauman, the C.E.O. of Viacom, and Les Moonves, the C.E.O. of CBS, and their executive teams as well as to shareholders of the two companies, because Redstone controls the majority of the voting shares of both. Should his bravado fail to impress the Grim Reaper, a series of events will be set in motion that could lead to the sale of CBS or Viacom or both and dramatically change the calculus in Hollywood. Needless to say, with so much at stake, nearly everyone involved—including Redstone’s 43-year-old live-in girlfriend, Sydney Holland, his close friend and former girlfriend, 50-year-old Manuela Herzer, and his daughter, Shari Redstone, a 61-year-old divorced mother of three, whom Redstone once called his heir apparent only to change his mind later—is jockeying for position as the king fades. “No one seems to have any definitive view on what happens,” says a longtime Hollywood executive.

In the meantime there are widely diverging accounts of the state of Redstone’s health. To address the question, the easiest thing would be to allow me a visit with him at his mansion. But Redstone is off limits to outsiders these days. For the first time in anyone’s memory, he did not attend the Viacom annual meeting, in Miami on March 16. But he is planning to attend this year’s CBS annual meeting, in New York on May 21. He attended CBS’s annual meeting last year, in Los Angeles, but only briefly, when, hidden by a curtain, he was carried onstage in a chair. He was on the November 2014 Viacom earnings call, but barely. His faint voice could be heard introducing Dauman: “Good morning, everyone. Here’s my wise friend Philippe.”