Even then, at a college of overachievers, Zucker stood out because of his determination. “The interesting thing to me,” recalls Conan O’Brien, a classmate who edited the Harvard Lampoon and will take over The Tonight Show next year, “is that there has been no change. I think he’s the same guy he was then. He could probably have taken the reins of NBC Universal then. He’s probably pissed that it didn’t happen then.” Many describe Zucker’s tireless enthusiasm, which won over his employers early in his career. “He has this charm,” says longtime NBC colleague Dick Ebersol, now the president of NBC Sports. Ebersol mentored Zucker after he landed his first job at NBC. “Even when he is pissing someone off,” Ebersol says, “he will usually, eventually, win them over.”

Zucker was famously the executive producer of the Today show at age 26. He helped Katie Couric become the most successful morning-show host ever and oversaw both the launch of Today’s concert series and the streetside studio, which became a central part of the show. His precocious and public success inevitably meant that his first missteps would be reported with glee. After he took over as president of the NBC Television group in 2004, prime-time ratings slipped 11 percent during his watch, dropping NBC from No. 1 to No. 4. Kurt Andersen of New York magazine declared NBC’s 2004–05 season an “annus horribilis.” Zucker’s widely publicized flops included the Friends spinoff, Joey, and the expensive animation show Father of the Pride. Much to his own surprise, Zucker became the poster child for failing upward, as he was promoted to C.E.O. of NBC in 2005, and then to his current job last year. “I was very young. I had a lot of success. I had a lot of coverage,” he says. “There was a tremendous amount of, you know—a lot of jealousy. It kind of goes to my idea that we live in a schadenfreude world.”

Critics have also slammed Zucker for his decision to pass The Tonight Show torch from Jay Leno to O’Brien, a deal made four years ago and one that Zucker insists is the correct call. He laughs when I ask him whether he regrets the move, considering that Leno remains a ratings champ. “You have to make these calls,” he says. “You’d rather make these calls a little too soon rather than a little too late.”

Zucker’s colleagues, competitors, and family all marvel at his competitiveness. “If you pick up a ping-pong paddle in our house, he will play you until he wins, even on a weekend,” Caryn says. “He won’t stop until he wins.”

Caryn and Jeff met in 1995 while getting coffee below NBC’s Rockefeller Center headquarters. Five minutes later, after returning to her desk at Saturday Night Live, she got a call from him asking her to lunch. “I had a boyfriend when I met him. I told Jeff, and he said, ‘You can still have dinner.’ Then he sent me flowers, kept telling me to get rid of the boyfriend, and he pursued me like a maniac. When he wants something, that’s it: one track. But it wasn’t done in a creepy, stalker way.”

Zucker has had not one but two bouts with colon cancer, during which he scheduled his chemotherapy for Friday afternoons so that he would miss as little work as possible. That is now part of the myth of the indestructible Zucker. But he received surprisingly little sympathy in the press.

Zucker says he has grown used to the criticism. “I’ve woken up in a hospital bed after surgery twice with staples in my stomach, in more pain than anyone should be allowed in their lives,” he says. “I’ve gone through chemo for nine months, vomiting my guts out afterward, then gone back into the hospital. If people want to take shots, hey, I’ve had more pain than anyone can give me.”

His weekend tennis matches at the East Hampton Racquet Club—he was captain of his high-school tennis team—are a proving ground for Zucker’s ego. He will soon undergo his second knee surgery, but he’s so committed to the sport that he will play through the soreness until then. “I don’t really know if he finds it fun,” Caryn says. “He really plays to win.”

Caryn says that Zucker’s claim that he sleeps only four hours a night is true. “He needs to be on the phone and on the BlackBerry at all times,” she says. “He never stops working. It never ends. Because it can’t. But I understand that. I don’t know if this kind of marriage could work for everyone, but I completely understand it, mainly because I used to work in television.”