LOS ANGELES—The SUV pulls to an abrupt stop on Ventura Boulevard in Studio City. In the middle of the westbound lane is a man in a loud shirt, his body coiled with energy, darting across traffic toward a strip mall.

The driver jumps visibly, and not merely at the presence of a human being on the pavement. It’s who that human is: Without the hasty application of power brakes, one of the most recognizable faces in the history of American television would have become one with the road.

But it’s lunchtime, after all. Good sushi is across the street. And a guy like William Shatner is not about to be stopped by something as mundane as traffic.

Why did William Shatner cross the road? Why has he ever? To get to the other side. To see what’s out there. To find out stuff and inhale the universe in his singular Shatnerian way. It’s the story of his life—and the lives of the characters he has breathed, spoken and shouted into existence over a 50-year performing career.

It’s the story of “Boston Legal” bombast Denny Crane, racing to experience all life’s pleasures before Alzheimer’s drags him not-so-gentle into that good night. It’s the story of the Priceline Negotiator, that discount-travel maniac who barnstorms across the planet to get us better deals on hotels and flights. It’s the story of James T. Kirk, the wise and womanizing starship captain who led a crew of 23rd-century explorers across interstellar backroads.

And it’s the story of Shatner himself—a man governed by his passions and interests, a man who crosses new roads every day, gleefully ignoring those who dismiss him and conquering frontiers he never dreamed possible. A cultural phenomenon who, despite tales of his galactic ego, seems strikingly down to Earth as he shapes and basks in the third golden age of his career.

“I’m trying to fill the cracks in the bricks that have been written. I’m the mortar,” he says. “That’s what an actor should be doing.”

Yes, he’s been pilloried over the years—perhaps justifiably here and there—for his roundhouse method-actor style, for his apparent obliviousness of his own over-the-topitude, for his primal, all-encompassing Shatnerness.

But being snide about William Shatner is so 1997. He is 77 now, post-post ironic, doing precisely what he wants to—and, finally, no longer terrified about making a living. “Live life like you’re gonna die, because you’re gonna,” he sang a few years ago. And he does: “There is so much going on with me right now, it’s difficult to believe all of it,” he says.

After the brutally honest 2004 album “Has Been” with Ben Folds, after the Emmy in 2004 and the second Emmy in 2005 and the new autobiography this spring, if you’re still stuck parodying Shatner’s staccato delivery and making T.J. Hooker toupee cracks, the joke, friend, is on you.

“Lemurs,” William Shatner is explaining through mouthfuls of sushi, “are primitive animals of many varieties.”

You name the subject, he’s fascinated. Global warming. Asian soap operas. The sentience of fish. Afghan politics. The turkeys he deep-fries in a “multimedia show” every Thanksgiving. And his timeless loves—his wife Elizabeth, his three daughters and his racehorses.

We always want our heroes to like us. So this much you should know: Shatner is one of my heroes. Has been ever since my sister put me down in front of an episode of “Star Trek” in 1969, when I was a year old.

Why? Because the guy lives large. He portrays decisive, humane, driven men. His emotion is his strength. He may be Canadian, but he exudes an American frontier spirit that he breathed into his most enduring alter ego so well that one of my younger son’s two middle names is Kirk. Don’t judge.

Fortunately for my own fragile inner toddler, Shatner is an excellent host, encouraging his guests—myself, a photographer, the marketing chief of Priceline—to consume every kind of raw fish on the menu. “Are you enjoying this?” he says more than once. “No—really. I want you to enjoy this.” In the background, John Denver is singing “You Fill Up My Senses.”

To sit and talk with Shatner over a meal is its own multimedia show. You start by marveling about the familiar voice you’re hearing. By and by, you begin paying attention to what he’s saying, which is a theme park of topics. This is a guy who, in his new autobiography “Up Till Now,” rhapsodizes about a gas station where he found “the finest tire air I’ve ever encountered.”

He has a conversational style—a cognitive style, even—of starting slowly, navigating his way into a topic and, in the course of a single sentence, transforming from cool introspection to full-on oratory.

This much-scorned, steam-gaining delivery is the product of a man thinking something through and finding conviction along the way. With Captain Kirk, it went like this: “Risk—RISK is our business. THAT’S what this starship is all about. That’s why we’re a-BOARD her!”

With Shatner, it goes like this: “We can’t wait for something dire to happen before this democracy decides to gird up and FIGHT global warming. We’re on ... a collision course ... with HIStory!” (This is followed quickly by, “Shall we order something else?”)

Joining us for lunch is Brett Keller, chief marketing officer at Priceline.com, where Shatner has been frontman for a decade, urging people to name their own price. Both sides have benefited: Priceline got an iconic figure to shape its brand, and Shatner got stock options and a forum upon which to surf back into the collective consciousness.

In the latest Priceline ads, Shatner bursts forth as the Priceline Negotiator, a mashup of James Bond and Ron Popeil who will do anything to help people broker better deals. Like most of us, Keller is both amused by and in awe of this star who came to a commercial shoot and started developing the character.

“You’re a celebrity (and) you’re asked to do a 30-second television spot. It’s not the most glamorous thing in the world. But he dives in,” Keller says. Market research, Priceline says, has shown an affinity for Shatner across age groups and demographics.

“Everyone knows William Shatner,” Keller says. “You either love him or you hate him, and I think most people love him.”

For the hecklers, Shatner has a message. Decades after his much-maligned album, “The Transformed Man,” boldly took “Lucy in the Sky With Diamonds” into strange new worlds, Shatner performed songs from “Has Been” before 4,000 cheering fans. He closed with “Lucy” and thrust a meaty digit skyward during the duration of the song.

It wasn’t his forefinger. It wasn’t his ring finger. It wasn’t his pinky, either.

He has always favored unusual paths. You don’t make an entire horror movie in Esperanto (“Incubus,” 1964) otherwise. You don’t open an equestrian camp to help disabled Israeli and Arab children get along. And you certainly don’t serenade George Lucas by dancing with stormtroopers while singing a personalized version of “My Way.”

Shatner has carved himself a unique place in the culture through a complicated blend of sincerity, bombast, wink-nudge irony and self-parody. Hate him or love him, rarely has an entertainer straddled giggles and glory so adeptly. And rarely does a performer have three distinct and separate careers, each building on the last:

• Shatner No. 1: I’m a Very Serious Actor. This one played tortured men in two “Twilight Zone” installments, a slick racist in 1962’s “The Intruder” and created the role of the iconic Captain Kirk in the original “Star Trek.” This Shatner was drama on steroids, and he endured through the 1980s with the tough-as-nails “Hooker” and a Captain-Kirk reprise in seven “Star Trek” movies.

• Shatner No. 2: I Laugh At Myself And You Can Too. Emerged around 1997. Shatner really jumped into self-parody in a 1997 film called “Free Enterprise,” in which he played a heightened version of himself. Then came his appearance as the alien leader on “Third Rock From The Sun” and his first Priceline ads, which cast him as a zeitgeisty, lounge-lizard joker.

• Shatner No. 3 : We Laughed Until We Cried. The most sophisticated Shatner of all.

For years, it was assumed that Shatner equaled Kirk. Then came Denny Crane, a Boston law firm’s rainmaker enduring the beginning of “the mad cow.” Denny is loudmouthed, sexist, self-obsessed and terrified at what age is stealing. Only his much younger colleague, Alan Shore, understands the panic behind the bluster.

Shatner as Kirk may be a memory. While Leonard Nimoy will be featured as an aging Spock in J.J. Abrams’ reboot of the “Trek” franchise next year, Shatner isn’t coming aboard; his character died in 1994’s “Star Trek Generations” and will be played in the new film by the young actor Chris Pine.

Other than that, all things seem possible. “I have all of the hungers and passions and desires of when I was 20,” Shatner says. “There’s nothing I can’t do.”