Scott Lang (Paul Rudd) assumes the Ant-Man mantle from Hank Pym in Marvel’s latest superhero film. (Zade Rosenthal/Walt Disney Pictures)

Paul Rudd probably wouldn’t make a casting agent’s short­list for a Marvel superhero. Even if you view the actor’s charm — worn less like a cape than a shrug — and his apparent agelessness as superpowers, his self-effacing, Everyman nature makes him an eccentric choice for a comic book character.

But then again, Ant-Man is not your typical, larger-than-life part. Possessing the ability to shrink to the size of an ant without altering his normal human strength, Ant-Man, on paper, sounds like a rejected idea from a desperate comic book writers’ brainstorming session. Never mind his ability to exercise telepathic control over actual ants. (Be still my heart.)

In the film “Ant-Man,” Rudd’s version of the obscure Marvel character — a hero first introduced in 1962 — makes for a perversely pleasurable combination of puniness and power. Telling the story of Scott Lang, a man who inherits the mantle of Ant-Man from the costumed crusader’s originator, Hank Pym (Michael Douglas), the movie deploys its real secret weapon: wit.

The second half of this nearly two-hour film is a pure delight — fast-paced and funny and filled with special effects and humor as great as any recent Marvel movie, with the possible exception of “Guardians of the Galaxy.” One of the film’s signature bits involves the disconnect between Ant-Man’s tiny heroics — which during the film’s climax take place on a child’s train set — and what those heroics look like to normal sized people. Ant-Man’s mighty struggle to heave a Thomas the Tank Engine toy, for instance, is contrasted with the resulting plasticky clatter as it skitters harmlessly across the floor, making for a sublime sight gag.

Getting to that point, however, requires a little patience. For its first 60 minutes, “Ant-Man” churns out a setup that is as protracted as it is necessary, given the novelty of the character and the audience’s unfamiliarity with his back story.

Actor Paul Rudd plays a superhero with the ability to change his size in Marvel's "Ant-Man," in theaters July 17, 2015. (  / Walt Disney Pictures)

Lang, a divorced dad, ex-con and recidivist cat burglar, is recruited by Pym, the aging inventor of a shrinking technology and the original Ant-Man, to don Pym’s old suit and go after a rival industrialist (Corey Stoll) who’s trying to sell similar miniaturization hardware to bad guys. Unfortunately, much of this prologue, which also deals with Lang’s bond with his young daughter (Abby Ryder Fortson) and his rivalry with his ex-wife’s new boyfriend (Bobby Cannavale), creeps along at a snail’s pace. Despite a visually clever sequence when Lang first tries on the ant suit — encountering such dangers as a giant vacuum cleaner and a cataract of water from a bathtub spigot — the first half of the film feels, at times, more like a relationship drama than an action movie.

All that ends when the action kicks in, ’round about the movie’s midway point. Once it does, “Ant-Man” turns into a rousing, “Ocean’s Eleven”-style heist flick crossed with a mini-“Mission: Impossible,” in which Lang and his army of six-legged ninjas attempt to steal the competing shrink-suit, dubbed Yellowjacket. (Fair warning: There are a number of scenes featuring CGI creepy-crawlies. To its credit, the “Ant-Man” supporting cast looks uncomfortably lifelike, presenting what could be a minor problem for the entomophobic moviegoer.)

It’s easy to see the appeal of the Ant-Man character to the film’s co-writer and original director, Edgar Wright, auteur of such quirky send-ups of genre film as “Shaun of the Dead” and “Hot Fuzz.” There’s a perverse magic to a hero whose un-Hulk-like, underdog status — the ability to bulk down, never up — is his strength, not his weakness. Although Wright dropped out of the picture last year after creative differences surfaced with Marvel, his replacement, director Peyton Reed, obviously respects the character’s paradoxical power.

It may take a while for the movie to wind up, but “Ant-Man” punches well above its weight.

PG-13. At area theaters. Contains sci-fi action violence and some rude language. 117 minutes.