Bill Murray, left, appearing on the first “Late Night With David Letterman” show in 1982. (NANCY KAYE/Associated Press)

Dan Zak is a reporter for The Washington Post and author of “Almighty: Courage, Resistance, and Existential Peril in the Nuclear Age.”

For me, it was the dialing music. “Paul, can we have some dialing music?” David Letterman would ask, and his band leader would twinkle a melody on the keyboard as the host plopped a rotary phone on his desk and began calling whomever: CBS chief Les Moonves; an office drone named Meg in a building across the street; his mom, Dorothy, in her kitchen in Indiana. The bit — can it be called a bit? — lasted mere seconds, until someone picked up the line, but the asking for and receiving of dialing music always made me smile. It was the Letterman ethos in a single moment: a shiny shellac of needless formality over the absurdity that defined his late-night comedy show.

On television, Letterman was both genial and depraved. In the span of one hour, he could ask for dialing music and then commission the destruction of an automobile by dropping bowling balls off the Ed Sullivan Theater. There was also something remote and unknowable about Letterman. He was a nimble entertainer and a world-class grump, a complete stranger with one of America’s most recognizable faces.

Jason Zinoman, in his definitive and enjoyable biography “Letterman: The Last Giant of Late Night,” demystifies the host. A comedy columnist for the New York Times, Zinoman walks the line between reportage and criticism, and shifts between historian, clinician and fan boy without grinding the clutch too much. His studious research is spiced by an enduring appreciation of Letterman’s work and salted by the cataloguing of the host’s less-savory traits and behavior: hypochondria, philandering, depression, mean-spiritedness, the occasional bout of creepiness and a terminal case of insecurity.

"Letterman: The Last Giant of Late Night," by Jason Zinoman (Harper)

So what makes Letterman “the last giant,” as opposed to his eternal rival Jay Leno, who beat him to the “Tonight Show” desk? There are two answers. The first is that Letterman is simply funnier. Choosing between Leno and Letterman was “a litmus test of whether or not you were the kind of person worth talking to,” Zinoman writes in his introduction. The second answer is formal in nature. The book maps, move by move, how Letterman’s 33-year run reinvented late-night television.

“He created a new comic vocabulary that expanded our cultural sense of humor,” Zinoman writes, “and made a persuasive case for the daily talk show as an ambitious art form.” Carson’s “Tonight Show” was entertainment. Letterman’s show was also art. Zinoman’s book is a serious (but lively) appraisal of that art.

The distinction between art and entertainment is embodied by Merrill Markoe, who is the oft-forgotten mother of Letterman’s career. Markoe, a writer, met Dave in 1978 at the Comedy Store, on Sunset Boulevard in Hollywood, and became a profound comic influence (and, for years, his girlfriend). She adored formal experimentation and was less keen on satire than on writing and producing comedy that baffled, disoriented and colored outside the lines. The couple created “The David Letterman Show,” a live morning program on NBC that lasted four months but established the foundation for their late-night run.

Markoe was responsible for segments like “Viewer Mail,” “Small Town News” and “Stupid Pet Tricks.” She pushed the host to do remotes, which sent Letterman out of the studio and into unpredictable public situations.

“Letterman was a powerful comic weapon,” Zinoman writes of the partnership. “Merrill supplied the bullets.”

In this way, the book is more a biography of a concept and its execution than of an individual and his evolution. As it should be. Zinoman divides Letterman’s TV career into distinct phases, but the book is just as gossipy as it is academic. Zinoman plots the outside cultural forces at work on Letterman’s shows and tags the people who used the host as an avatar for their own comic sensibilities. Besides giving Markoe her due, Zinoman honors the contributions of director Hal Gurnee, who brought a fast-moving and ever-changing visual rhythm to the otherwise staid late-night format; featured player Chris Elliott, whose volatility was a combustible foil for Letterman’s eternal nonplussedness; and writers such as George Meyer, a comic essentialist who proposed what Letterman later called “the single most brilliant idea on the show ever”: a contest between a humidifier and dehumidifier.

Like an anthropologist, Zinoman plots Letterman on a continuum, describing — without sounding like an encyclopedist — how “Tonight Show” hosts Jack Paar and Steve Allen set the stage for him; how Letterman first thrived as the dark, ironic counterpoint to Reagan’s “morning in America”; and how this, in turn, prepared the world for the incisive comedy of “The Simpsons,” Garry Shandling, “Seinfeld,” Tina Fey — and for any art or artist that thrives on the inane and the self-referential, the subversion of his or her chosen medium for the sake of its ennobling.

At no point, however, does Letterman seem like the giant of the book’s subtitle, at least not in a reverential sense. Two years after Letterman’s retirement, and especially in this era of Jimmy Fallon’s tranquilizing vapidity, Zinoman’s great achievement is rendering Letterman as utterly human, even subhuman at times, and charting his show as an irregular comic pilgrimage — if not toward comic excellence than at least toward comic insolence. The “last” in the subtitle rings truest: Letterman and company were pioneers, and new territory only gets discovered once.

Letterman
The Last Giant of Late Night

By Jason Zinoman

Harper. 344 pp. $28.99