Even as a kid growing up in the ’50s, Harvey Pekar was a true square peg, a nerd ready-made for ridicule, between his strange-sounding surname and obvious oddball tendencies (like going trick or treating without a costume). As an adult, the self-described “nobody flunky” settled into a soul-crushing job as a file clerk at the Veterans Administration Hospital in Cleveland, which would eventually inspire him to write the celebrated underground comic book American Splendor, an amusingly deadpan tome based on his drab, stuck-in-a-rut life.

The movie made from the American Splendor series, written and directed by Shari Springer Berman and Robert Pulcini (who made a documentary about cemeteries, The Young and the Dead), is a compulsively watchable, wry and witty portrait of the slovenly, perpetually scowling author (played by Paul Giamatti, lately of Confidence). “I’m desperate, lonely and horny as hell,” Pekar says ruefully, painfully aware that his rotund body, bulging eyes and bushy eyebrows don’t exactly make him a babe magnet.

Though Pekar is an atrocious artist — he can’t even draw a straight line, as the joke goes — his stories catch on, and he becomes an unlikely spokesman for society’s forlorn Average Joes and Janes. (“It’s about time that people who get picked on get to be heroes,” he says with relish.) His friends and co-workers love appearing as characters in his comics, but even after eight issues of American Splendor, he can’t afford to quit his day job because his royalties are so marginal.

In Joyce Brabner (Hope Davis), a frumpy comics dealer from Delaware, Pekar finds a combination cheerleader, wife and muse. With Joyce at his side, his career seems to take an upswing, climaxing with a string of appearances on Late Night With David Letterman. (“I felt like a sell-out,” he would later grouse.) When he is diagnosed with cancer, Brabner inspires him to turn his private battle with the disease into a very public graphic novel (incorporated into the screenplay) that goes on to win “a coupla National Book Awards.”

With very little money at their disposal, Berman and Pulcini have expertly captured the depressing, drab but often hilarious world of the terminally insecure Pekar, who at 63 still worries about where his next paycheck will come from. Their use of comic book conventions (captions, thought balloons) is exceedingly clever, as is their idea to feature the real-life Pekar and Brabner (and other people from Pekar’s life) in documentary-like moments that add an extra layer of irony to the already highly ironic material. At its best, American Splendor echoes Terry Zwigoff and Daniel Clowes’ terrific Ghost World, which revolved around two fashionably glum high school girls with a penchant, like Pekar, for all things negative and sour.

The film’s entire cast is good, especially Davis (also outstanding this year in The Secret Lives of Dentists) and Judah Friedlander (as Harvey’s Super Dweeb best friend, Toby). But American Splendor belongs to Giamatti, a New Yorker long on the brink of stardom (Storytelling, Planet of the Apes). Giamatti may not look or sound anything like Pekar, but it’s clear he understands what makes the balding, working-class, gloom-and-doomsayer tick. His inspired performance is destined to put the 36-year-old character actor on the map, perhaps even make him a (minor) household name. Sort of like Pekar himself.

American Splendor is playing at Landmark’s Hillcrest Cinema. For more information, call (619) 299-2100.

Kyle Counts is film critic for the Gay and Lesbian Times.