NEW YORK (AP) ― After being fired as NBC entertainment president toward the end of the “must see TV’’ period in 1998, Warren Littlefield packed photos, papers, awards and other memorabilia into a self-storage unit and turned the key.

For 10 years he paid the rent and never stopped by. Finally he unlocked the vault and began combing through the boxes ― a process of rediscovery that eventually led to his new book, “Top of the Rock: Inside the Rise and Fall of Must See TV.’’

Jerry Seinfeld, Kelsey Grammer, Lisa Kudrow, Anthony Edwards and Debra Messing are among more than 50 people who help Littlefield tell inside stories about “Seinfeld,’’ “Friends,’’ “Frasier,’’ “ER,’’ “Will & Grace’’ and what went on within NBC to make its Thursday night lineup the most powerful one in television during the 1990s.

“It was a very good decision for me to live in the present and not in the past, but after 10 years I thought, ‘Wow, the past was wonderful. And it’s worth celebrating,’’’ he said.

He had intended it to be a narrative, but instead the book takes an oral history format. Littlefield found the interviews so insightful and entertaining he felt it was best to quote from them.

“I was the network president,’’ Littlefield said. “I thought I knew everything. In every single interview, something was revealed to me and I thought, ‘Why in the hell did I never know that?’’’

There are plenty of fun inside stories, like when Noah Wyle of “ER’’ recalled being introduced to Rebecca De Mornay at a party for what he thought was the first time, only to be tartly informed by the actress that she had done six “ER’’ episodes and they had even shared a sex scene.

The six actors from “Friends’’ all had dinner with veteran director Jim Burrows in the middle of a Las Vegas restaurant before the first episode aired and he urged them to look around, that they’d never have the anonymity to do the simple thing of dining together unnoticed again.

Littlefield said he wrote the book for fans, not for score-settling or vindication. To the latter point, the facts speak loudly enough.

Even a decade ago toward the end of their runs, “Friends’’ and “ER’’ routinely reached more than 20 million people, sometimes approaching 30 million. This spring, shows on NBC on Thursday night are usually seen by between 2 million and 3 million people. Maybe half of that decline would be expected, since more competition and new technology make for lower television ratings overall.

Since Littlefield conducted all of the interviews for “Top of the Rock’’ himself, it was surely awkward when Jack Welch, former head of NBC’s parent company General Electric, explained that Littlefield was fired because executives felt he was a “dry hole.’’

In the book, Littlefield methodically details the billions of dollars in revenue earned by NBC’s top shows in his era, comparing it with the network’s current standing.

“Not bad for a dry hole,’’ he writes.

Littlefield is an independent producer now, quoting “Seinfeld’’ in saying he enjoys the opportunity to be “master of his own domain.’’ The job offers freedom, but his business is now dependent on people who hold network jobs like the one he once had, including some who cut their teeth at NBC in the 1990s.

He said he’d “never say never’’ about working for a network again, but isn’t expecting or angling for it. At a time of DVRs and dozens of networks making original programming, being an entertainment chief is harder than it was, he said.

He doesn’t think a network will ever be able to dominate one night so thoroughly and for so long. Asked what NBC needs now to turn things around on Thursdays, he answers: “Modern Family.’’ Specifically, it needs a buzzworthy hit with broad appeal that the network can build around.

He said he hopes current NBC Entertainment Chairman Robert Greenblatt can succeed.

“There’s a lot of opportunity,’’ he said. “There’s a lot of real estate. Hopefully with the right strategy and philosophy, they become stronger and more viable. That’s good for everybody.’’