Zucker, 42, assumed control of the vast media conglomerate that is NBC Universal 18 months ago after being elevated from his position as head of NBC’s television group, where he had worked for nearly 20 years—he started as a researcher for NBC Sports in 1988. NBC Universal is a behemoth comprising not only the NBC broadcast network but also cable channels Oxygen, Bravo, USA, and Telemundo; news channels CNBC and MSNBC; local television stations; a film studio; and theme parks. But it will be Zucker’s efforts to reconceive NBC, long one of the most reliable and profitable media businesses, that will define his tenure. Virtually every ­communications-technology breakthrough of the past 20 years, from the internet to TiVo to handheld playback devices and YouTube, has served to chip away at network television’s vast audience. Gone forever, Zucker will tell you, are the All in the Familys, the Friends, the Mary Tyler Moores, those great, fit-for-every-demo sitcoms that sucked up huge audiences and delivered vast swaths of advertising-friendly viewers. “It was a lot simpler back then,” Zucker laments, “when there were three networks and you could run your programs once and repeat them twice and that’s all you had to worry about.”

Lately, NBC’s prime-time operation has been underperforming even in the underperforming broadcast-TV sector: It was dead last among the top four networks when Zucker took over in 2007, and a year and a half into the Zucker era, it’s still dead last in the key 18-to-49-year-old demographic. Zucker and his staff are quick to point out that the network has remained profitable despite the ratings disappointments. In fact, the three years that Zucker was running NBC Entertainment, before he took over all of NBC Universal, were the most profitable in the history of the division. They also note that the network today makes up less than 5 percent of NBC Universal’s earnings; the cable division brings in the largest chunk of revenue.

But the network’s prime-time lineup gets outsize attention, given its relatively small contribution to the company. It’s the most damaged part of a broken business, as viewer loyalties to once-sacred time slots have disappeared. It’s also easy to keep score with prime time, because ratings come out every morning and reveal which network—and mogul—won or lost: NBC (Zucker), Fox (Rupert Murdoch and Peter Chernin), ABC (Bob Iger), or CBS (Les Moonves). “Zucker needs to turn around NBC prime time,” says a television executive who does substantial business with NBC. “He just does. It’s corporate bragging rights. It represents peacock prestige.”

The Rockefeller plaza corner office in which I meet Zucker is vast, with views of the Empire State Building from the three oversize windows facing south, and two windows facing east. Along the windowsills are photos of his wife, Caryn, a former associate producer at Saturday Night Live, and their four children: Andrew, 10, Elizabeth, 7, Peter, 5, and William, 2. This is a handsome family, and Zucker is happy to acknowledge that the kids take after his wife rather than him. A large ficus plant sits in the corner next to a Modernist steel peacock sculpture that faces Zucker’s imposing Art Deco desk. He is seated now in an overstuffed wing chair that has lion’s-paw feet and fabric decorated with fleurs-de-lis. As he talks, he crosses his legs. When he sits back, his feet actually lift off from the floor a bit, like a boy taking a turn on someone else’s throne.

Zucker has an appealing, ruddy tint that lends him a cherubic appearance, despite his gray pinstripe gabardine suit and linen shirt. He has wire-frame glasses and a fringe of graying brown hair. His stubble looks like the kind that grows in fast, but his five-o’clock shadow does little to lend him gravitas. He has a gift for appearing at ease and makes the occasional self-deprecating joke. More important, he comes across as surprisingly down-to-earth for a 42-year-old multimillionaire who recently bought Kitty Carlisle Hart’s former apartment on the Upper East Side.

Zucker’s height is much commented on: He is about five foot five. Yet that relative diminutiveness has perhaps made him more likable. Ever since he ran for North Miami High School ­student-body president with the campaign slogan, “The little man with big ideas,” he has known that to be noticed, to thrive, he has to be more winning, more persuasive, more determined than his average-size peers. At Harvard, where he was president of the Harvard Crimson, he was seen by one of his classmates as “not a great people person. He already had a great ear, but he hadn’t yet developed the people skills.”