Given the irony that saturates his humor like blood in a sponge, it’s fitting that the very title of this Salon People department makes something of a mockery of David Letterman at this stage of his life. After all, how many of you would agree, in 1999, that he has had a “brilliant career”? Looked at one way, Letterman has blown it. He lost out to Jay Leno in his quest to replace his hero, Johnny Carson, as host of “The Tonight Show,” a failure documented in Bill Carter’s 1994 book “The Late Shift,” among whose many fascinating details was the fact that Letterman campaigned for the position by not campaigning for the position. It wasn’t a matter of hubris, but rather the fact that it is simply not in Letterman’s character to seek the favor of anyone, be it audience or network brass. (In Carter’s book, Letterman assumed that even the execs he calls “weasels” would, through some combination of common sense and loyalty, give him the promotion he deserved.)

Since his subsequent move to CBS, Letterman hasn’t beaten Leno since 1995, when Hugh Grant, fresh from a prostitution bust, gave Leno the exclusive interview that, for reasons that still beggar the imagination, put Leno’s ever-increasingly dumbed-down, carny-show version of “The Tonight Show” on top of the late-night ratings heap and have kept it there ever since. Then there was the 1995 Oscar fiasco, when Letterman’s hosting strategy — a disastrous blend of New York-style lordliness and a misguided faith in the silly-absurd (“Oprah, meet Uma; Uma, meet Oprah …”) — left most of the Hollywood audience, accustomed to a night of un-ironic stroking, glaring grimly and unamused. Add to this the fact that “Late Night With Conan O’Brien” and Letterman’s own new follow-up act, “The Late Late Show With Craig Kilborn,” trade on youth-cult references that frequently make “The Late Show With David Letterman” seem more like the Rest Home Where Bart Simpson’s Grandfather Lives, and you’ve got yourself one aborted show-business trajectory. Anyone for clicking on “Stalled Careers”?

But what I’ve sketched out above is merely the conventional wisdom on David Letterman, the interpretation put forth nowadays by most TV critics, industry observers and more than a few Leno fans. This is the view of Letterman from those who’ve stopped watching him; who are perennially more interested in following whoever’s getting the most media ink or attracting the biggest ratings; who, indeed, didn’t cotton to Letterman’s ironic take on the talk-show role in the first place. I propose an alternative reality to everything stated above — namely, that David Letterman is, right now, as funny as he’s ever been (ratings be damned); that he is certainly the most important talk-show host of his era and arguably second only to Johnny Carson as the best of all time (more on Steve Allen and Jack Paar in a bit); and that Letterman — and I’m convinced you can date this from the moment he flicked his contact lenses in the garbage can about 18 months ago and started wearing those little wire-rimmed glasses — has jettisoned the dulled weapon of irony and is currently engaged in a kind of comedic guerrilla warfare that, if you were to pencil in a goatee on his face to complement those tiny spectacles, would render him the Leon Trotsky of Talk Shows: The Last Late-Night Revolutionary.

He is, of course, a highly unlikely anarchist. Born in on April 12, 1947, Indianapolis, to parents Joseph (a florist) and Dorothy (a homemaker), Letterman and his two sisters (one older, one younger) led the Midwestern idyll that breeds either contentment or wackiness, and in Dave’s case, wacky won out. This, despite the fact, as he once told Maureen Dowd, “My mother, bless her heart, was the least demonstrative person God ever breathed life into.” (Watching Dorothy over the years playing prim straight woman to many of Dave’s stunts, including sending her to the Olympics as a correspondent, you have no trouble believing she is one cool customer. Gee, do you think this had any effect on the formation of Dave’s own renowned reserve?) Letterman majored in semi-pro fooling around at Ball State University in Muncie (1965-70), hamming it up as a communications major on the campus radio station and on local TV. During his college years he also found time to marry, at age 21, fellow student Michelle Cook. The union collapsed in 1977 after the pair moved to Los Angeles, and Letterman has always taken the full blame: He was immature, too consumed with jump-starting his career. It’s the real-life version of what Carter described in “The Late Shift” as Letterman’s “penchant for self-denigration, no matter what was going on in his career.”

Letterman was born early enough to appreciate a folksy radio host like Arthur Godfrey, an early hero, and he thoroughly absorbed the deconstructive self-consciousness that Steve Allen brought to his reign over “The Tonight Show” from 1954-57. (Where Allen once covered himself in tea bags and had himself dunked into a cup of hot water, Letterman would later bedeck himself with Alka Selzer tablets and lower himself into a giant glass of water for some fizzy fun.) Talk shows were always Letterman’s goal. To break in, he went the Hollywood comedy-club route with moderate success; the consensus seems to be that he had cutting jokes and thinly veiled contempt for two-drink-minimum bozos — not the sort of recipe for a contented stand-up.

But, he once said in a rare flash of candid careerism, “You just use the clubs as a steppingstone.” He put in his time in TV hell — appearances on “The Gong Show” and “The $20,000 Pyramid”; a little stiff singing and dancing on Mary Tyler Moore’s ill-fated 1978 variety show “Mary”; a guest role in a 1979 “Mork and Mindy” that actually required him to approximate acting. All the while, he was plotting his own talk style. He had little use for the naked emotionalism of the other great host of his childhood, Jack Paar (who “Tonight”-ed with wracked sobs from 1957-62); no, Dave wanted to be like his Midwestern-born idol, Johnny Carson, who since taking over in ’62 had turned “The Tonight Show” into a well-oiled (and sometimes excessively oily) machine gleamingly efficient at both star-coddling and star-grooming. To do stand-up for King Carson was to be anointed a punch-line prince, and Letterman received the blessing after a sharp set in November 1978. Even then — no mere John Byner, he — Letterman was giving off the right vibes, and he ended up guest-hosting for Johnny 20 times before NBC said, Give this smart-aleck his own show.

Unfortunately for Letterman, that show was in the morning, a time of day when viewers were unaccustomed to countenancing the sort of amiably ramshackle, anything-can-happen show Letterman devised; people were confused by a semi-regular guest, housewife Mrs. Marv Mendenhall, who was actually an amusingly prissy character played by actress Edie McClurg. “The David Letterman Show” premiered in June 1980 and was canceled in October. NBC and Carson, a strong ally, kept the comedian on retainer until 1982, when, on Feb. 1, “Late Night With David Letterman” premiered, slotted after “The Tonight Show.”

This was, in the memories of many, Dave’s golden era, with characters like portly dumb-dumb Larry “Bud” Melman, show writer Chris Elliott’s “Man Under the Seats” and a vertiginous episode broadcast upside down. Working with a shrewd, cutting writing team that included then-girlfriend Merrill Markoe, Gerard Mulligan, Matt Wickline, Steve O’Donnell, Randy Cohen, Jim Downey and Tom Gammil, Letterman was doing the most innovative, ironic comedy on the air. Some guests have always responded avidly to Letterman’s blithe contempt for show-business obeisance, recognizing in his irreverence an opportunity to snub it themselves: Personalities as various as Bill Murray, Steve Martin, Paul Newman, Alec Baldwin, Bonnie Hunt, Kevin Kline, Drew Barrymore, Matthew Broderick and Tony Randall have all proven delightful company, game for anything Dave wants to throw at them and often giving him more than he bargained for. (Insert your own Drew-showing-him-her-boobies joke here.) Others have taken offense at his refusal to play the chattering flatterer (Cher), or taken the offensive to fend off his sarcasm (Madonna’s expletive-filled appearance).

“Hey, I’m no armchair historian,” Scott Dikkers, editor of the Onion, recently told the New Yorker, “but it was Letterman who made the world a sarcastic place. Because of Letterman, everybody I know is sarcastic all the time, in everything they say — never genuine.” This remark gets to the heart of Letterman’s legacy and his present-day dilemma. The sarcasm Dikkers speaks of, the pervasive irony that informed every second of Letterman’s NBC show, was so influential throughout television and pop culture in general that it has, by now, exhausted itself. And at times, it’s seemed to have exhausted Letterman himself.

“We know the show is tired; it’s the same crap night after night,” Dave fairly roared one evening this past September, sitting at his desk. “But here’s the thing,” he said, turning to the camera with a grin whose twitchiness slid somewhere between arch playfulness and suicidal self-contempt: “We just don’t care.” Seven months later, on a balmy April night, Letterman sauntered out onto the stage of the Ed Sullivan Theater, waved away the cheers, took his limbering-up, touching-his-loafers bow and said, “I’m Dave Letterman, I’m the host of ‘The Late Show,’ and you think you’ve got a rotten job.” The sense that Letterman genuinely believes he has — that is to say, does — a rotten job has been evident in the past: usually whenever he’s not talking about how miserable he is, when he’s smiling gap-toothily and throwing himself into comedy bits with zesty enthusiasm. Letterman invariably signals his disenchantment by feigning a chipperness so awkwardly that it is instantly perceived as false.

At his truest, he is a worrier, a fretful perfectionist and the most neurotically modest Manhattan person-of-note since New Yorker editor William Shawn. (He shuns interviews, parties, even off-camera palaver with celebrities — his commercial-break frostiness was lifted brilliantly by Garry Shandling on “The Larry Sanders Show” as one of Larry’s salient traits. At the same time, Letterman is a generous donor to charitable causes, loves dogs and cars, likes kids and audience members who don’t live in Manhattan or Los Angeles and was notably humane to Margaret Ray, the woman who stalked him for years, right up to her suicide in October 1998.)

But it’s when the quality of Letterman’s show is high, as it has been over the past year or so, that he feels freest to indulge his favorite comic persona: that of the cranky misanthrope, the whining complainer, the middle-aged, Midwestern goofball who likes to use the power his show has to promote big-name guests to, instead, cut those stars down to size. Letterman still will brook no pretensions or banal product plugging — when you come on Dave’s show, you’d better have a few choice anecdotes that don’t have to do with your current movie project, lest the host end your segment with a quick cut to a commercial. But he resorts less and less to the bullying and cajoling that used to characterize his interviewing style. Over the past year, he’s shown more of an interest in engaging guests in serious discussion (New York Mayor Rudy Giuliani seemed caught off-guard when Letterman pressed him on police brutality recently), yet without going all Charlie Rose on us.

Once again, Letterman is going against the prevailing style. Let Kilborn, O’Brien and Jon Stewart (“The Daily Show”) continue to strip-mine irony ore; except for the often exhilaratingly loony O’Brien, their styles already seem tired. Letterman, by contrast, currently seems more comfortable in his own leathery skin, and — even as he continues to sink in the ratings — his show is all the better for it. With the irony burned off, his comedy now breathes fresh oxygen; he’s getting big laughs by doing things like revitalizing old forms, such as an entire monologue consisting of “It was so hot today” gags (“It was so hot today, the rats at Dunkin’ Donuts moved over to Ben & Jerry’s” — badda-boom! rim-shoots Paul Shaffer and the band, Vegas-style.) I warn you: Years from now, when Dave has retired to Indianapolis to jog 10 miles a day and wave the first-race flag for the opening of the Indianapolis 500, you’ll all be moaning about what a loss he is to television, just like all those weepy keepers of the Carson flame. For a guy whose current favorite catch phrase is “I wouldn’t give your troubles to a monkey on a rock,” Letterman is one monkey who’d turn into your favorite uncle if you gave him half a chance.

Pauline Kael sounded like Pauline Kael right off the bat. When she was just starting out as a movie critic in the ’50s, doing radio reviews of movies for the Berkeley, Calif., public radio station KPFA and writing program notes for the city’s revival houses, she was already tossing off unpopular barbs (“I would like to suggest that the educated audience often uses ‘art’ films in much the same self-indulgent way as the mass audience uses the Hollywood ‘product,’ finding wish fulfillment in the form of cheap and easy congratulation on their sensitivities and liberalism”) and she was already combative (“My dear anonymous letter writers,” she said during one broadcast, “if you think it so easy to be a critic, so difficult to be a poet or a painter, may I suggest you try both? You may discover why there are so few critics, and so many poets”). She was already looking at the big screen for the big picture (“If you hold the San Francisco Chronicle’s review of ‘Breathless’ up to the light, you may see H-E-L-P shining through it.”)