Few could claim a perfect record at bedding all the Maxim cover girls in a given year. Even fewer still could do so in a cliffside Malibu mansion. And even fewer still would brag about said conquests to friends they’ve given such playful nicknames as “platypus” or, stranger yet, “sally patch.”

Yet there’s Tony Stark, privileged playboy cynic and ridiculously rich weapons manufacturer, doing all three. And that’s before he dons a shiny and sturdy titanium outer shell as Iron Man.

Stark sure seems like a hard hero to identify with, but as presented in Iron Man, adapted from Marvel’s comic, his actions are entwined with his hallmarks of humanity. Stark’s powers are manmade, born of gearhead curiosity and a mournful reflection on his past. His bravado boosts his broken soul, and only through remorse and guilt will that gradually crystallize into heroism.

In other words, it’s the perfect part for Robert Downey Jr. He’s as unlikely a blockbuster star as Stark is a hero, and yet Downey’s winning combination of conscience and craziness makes Iron Man just as tight and thrilling in its characterization as in its high-flying action sequences.

Working on his largest film yet, director Jon Favreau displays the same wonderment and control over visual effects as he did in 2005’s underrated Zathura. Excepting a clunky flashback prologue and a mishandled escape sequence, it’s a flawlessly paced origin story with humor, smarts and soul.

The film opens with Stark — prodigal-son heir to a military-contracting empire — rolling with an Afghanistan convoy of American soldiers, for whom he’s just touted the ultra-destructive Jericho missile system. A horrific ambush ensues, and Stark scrambles from the chaos only to watch one of his own bombs explode in his face — its shrapnel piercing his chest and poisoning his heart. It makes for a humdinger of an opening, but an awkward flashback to introduce Stark’s wild lifestyle interrupts an otherwise lean, linear approach.

Terrorists capture Stark, saved only by a crude electromagnet keeping the shrapnel from his heart. They force him to build Jericho missiles for them but, aided by a doctor (Shaun Toub) imprisoned with him, Stark starts building a heavy suit of iron armor fortified with armaments to escape. It’s hard to believe terrorists — especially with a closed-circuit camera system — would allow Stark to work unchecked, and the not-quite-great escape has a diminished sense of danger.

Stark abruptly shuts down his weapons division after his near-death experience, and the move draws ire, respect and loyalty from the three main people in his life. Stark long ago edged out his late father’s business partner Obadiah Stane (Jeff Bridges) for controlling interest in the company. Pepper Potts (Gwyneth Paltrow) is his long-suffering assistant who quietly pines for him. And Jim Rhodes (Terrence Howard) is his unwavering flyboy pal through thick and thin.

Faced with both this new technology and a lease on life, Stark begins refining the iron suit — which initially resembles an overfed Rocketeer with a clubfoot — into something sleek, fast and airborne. Not even Stark knows his intent at first, but growing atrocities in the Afghani region from which he escaped and Stane’s increasingly hostile takeover bid point him in the proper direction.

There’s no more entertaining live-wire actor than Downey to guide this story, and he’s perfectly complemented by his supporting cast. With shaved head and beard, Bridges resembles a Grecian bust, and he reserves his rage for one mighty roar near the end. Howard infuses a boilerplate buddy role with a rowdy streak certain to surface in sequels. And with personality and class, Paltrow reclaims comic-book redhead territory after Kirsten Dunst stunk it up in the Spider-Man films.

Favreau (who starred in Swingers) also shows he hasn’t forgotten his comedic roots with scenes of debauchery on Stark’s private plane, a human Operation moment between Downey and Paltrow and slapstick grace notes from the robotic-arm aides de camp in Stark’s lab.

Yet he’s also able to deliver briskly exhilarating action sequences — Stark’s flight test (tied into his own limit-pushing mentality), Afghanistan infiltration and fighter-jet dogfight. Each is so crisply satisfying that a finale resembling a 100-calorie version of Transformers is fairly anticlimactic. (If you’ve seen one massive energy beam shot into the sky, you’ve seen them all.) But the film’s overall effect is of ironclad accomplishment, for which a handful of sequels would be welcomed.