David Letterman and Jay Leno's late night rivalry detailed in explosive new book

In his new biography, "Letterman: The Last Giant of Late Night," author Jason Zinoman details the infamous late night rivalry between David Letterman and Jay Leno throughout the '90s and '00s.

In excerpts obtained by People, Zinoman details how Leno was able to snag the gig as host of "The Tonight Show" in 1991 upon Johnny Carson's retirement over Letterman, and Letterman's subsequent reaction to the news.

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"Letterman assumed one day he would get a call from Carson or the head of NBC to offer him the job. It never happened," Zinoman revealed in his book. "Rick Ludwin, head of late-night programming at NBC, respected Letterman as a great entertainer but was skeptical that he could draw the broad swath of viewers that made up the 'Tonight Show' audience."

Not only that, but Ludwin "also saw Letterman as difficult to deal with. Whereas Leno was friendly and approachable, Letterman was distant, even hostile."

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In response to the snub, Letterman "decided that [he] didn't like [NBC president] Warren Littlefield because [he] didn't get 'The Tonight Show.'"

"I blamed the whole thing on him, rather than taking responsibility for myself," Letterman admitted.

Zinoman wrote in "The Last Giant of Late Night" that this kind of anger wasn't uncommon coming from Letterman. In fact, it was more normal than not for him to be unhappy with someone or something.

"Everyone is born with an emotional thermostat," writer Steve Young told Zinoman. "You can nudge it up and down, but it will always revert to its natural setting. His was that he was never truly comfortable unless he was seething with unhappiness at something."

"Letterman: The Last Giant of Late Night" by Jason Zinoman hit bookshelves on April 11.

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