Stewart Brand, techno guru, counterculture impresario, inspects my ragtag clothes, spots the cotton long-underwear shirt I've layered beneath a fleece.

"Cotton is the stupidest thing you can wear on the mountain," he says matter-of-factly. We're hiking Mount Tamalpais, Marin County's highest peak, just north of the Golden Gate Bridge and not far from where Brand lives. Luckily, it's 45 degrees out, with little chance of hypothermia. "You could die," he tells me.

We break for water sometime later, at a clearing overlooking the San Francisco Bay, which this morning is enveloped in a mossy blue fog. The 74-year-old Brand, who has long, angular features and in his safari hat resembles a craggier Crocodile Dundee, demonstrates in a blur of motion how fast he can shed his GoLite pack and draw a knife from a sheath on his right hip. Other hikers sometimes don't follow the rules, he explains, and let their dogs run off-leash.

"Have you ever, you know, had to put one down?" I ask, curious to plumb the depths of Brand's practicality. It is no great shock that the editor and publisher of the Whole Earth Catalog – the atlas-size compendium of "tools" that Brand started in 1968, a publication Steve Jobs once called a "Google in paperback" and "one of the bibles of my generation" – would outfit himself with an array of useful instruments. But I didn't anticipate his wielding one with such martial purpose.

Brand says a dog did charge him once, and – knees bent, his left arm crooked into a shield – he had reached with his right hand for the blade. But it came up empty. He had left the knife on his dresser.

"The aggressive act was enough to show him who was alpha," he says. The dog slunk away, tail tucked.

Brand first came to national attention in his twenties, promoting – and enjoying – the liberating powers of LSD as one of Ken Kesey's Merry Pranksters. Over the next half-century, Brand proved to be an endless purveyor of information and invention, a constant catalyst of activity and surprising assemblies. A Sixties icon, he has also shaped our culture in each successive decade.

With the Whole Earth Catalog, which was filled with thousands of short appraisals covering everything from hydroponic farming practices to electronic music, stretching techniques, windmills, and even early personal computers, Brand defined a countercultural ethos that became what is now, essentially, the mainstream. Today, practically all the items covered in the Catalog are available at the click of a mouse; back then, it was an invaluable resource for the country's growing ranks of environmentalists, do-it-yourselfers, and back-to-the-landers. Maybe more revolutionary was that the Catalog combined ecological mindfulness with a belief in the transformative power of technology. In its pages, Brand showed that entrepreneurship and consumerism could also bring power to the people. After all, the kind of activities for which the Catalog provided in-depth instruction – building your own cabin or starting a commune – might just require the purchase of a few products, and that was going to take cash. "Whether you survive in those circumstances," Brand says, explaining his view of self-reliance, "very much depends on your understanding of money." The Catalog didn't simply ground the era's "turn on, tune in, drop out" ideals in the real world – it provided the millions whose minds had been blown open the practical tools to make that world anew. "What we were really was counter-counterculture," Brand says as we continue our ascent.

There were always computer guys hanging out at the epochal Bay Area parties, drawn, no doubt, to the psychedelics but also to Brand. "That Stewart was so at home in the world of computers baffled us," says Brand's friend Gurney Norman, a former Merry Prankster as well as the 2010 Kentucky Poet Laureate. "The rest of us sat around trashing IBM and big business, believing computers symbolized something evil," he adds. "We were so dumb."

Kevin Kelly, a founding editor of 'Wired' magazine, credits Brand with finally turning hippies on to the computer, showing it to be another human-scale tool, a better means than drugs to human augmentation and expanded consciousness. "Stewart brought together personal enlightenment and the personal computer," Kelly says. "Today, the Bay Area is all about the fusion of those two things. What seemed so contradictory in the Sixties is now so obviously complementary."

In the 1990s, Brand helped create the Long Now Foundation, a think tank that adopts a 10,000-year outlook to foster responsible future behavior. The group continues to hold seminars each month, with talks by Silicon Valley executives, academics, futurists, and historians; the foundation is also developing an online archive of the world's 7,000 known human languages. Jeff Bezos, founder of Amazon.com, is letting Brand build, on his West Texas estate, the "Clock of the Long Now" – which is, well, an actual 200-foot clock that will keep time and sound a unique chime in a different sequence each day for the next 10 millennia as a physical incarnation of the group's ideals. Brand believes that the 10,000-year time frame holds, perhaps, an unlikely appeal to the captains of dot-com industry. "These are the people surfing Moore's Law," he explains, citing the notion that computer processing power doubles every two years. "They're intensely convinced that things are moving faster and faster. So they feel the need to balance their lives and thoughts with something large-scale and long-frame."

At 2,350 feet, we take a break beside the remnants of "The Crookedest Railroad in the World," a 19th-century train that once brought sightseers up the mountain's switchbacks to this very spot. By now, I expect Brand to wow me with yet another gadget. He does not disappoint, placing on a picnic table before us what looks like a miniature rocket launcher. He twists it onto a thermal mug rigged with a French press, fires up a tiny propane tank, and, minutes later, pours me a cup of coffee.

As we sip our drinks, I bring out my notebook and read a question from a long list I've prepared. Brand raises his face to the sun and closes his eyes, remaining like that for nearly a half-minute without uttering a word. He looks so convincingly becalmed that I wonder if he's nodded off. I'm about to nudge him when Brand's eyes pop open, and he delivers a well-considered reply to my query, the subject of which I have by then forgotten.

"I'm allergic to repeating myself," he says, by way of explaining his not-uncommon reflective silences. "I'm going to raise awareness about, say, the importance of nanotechnology, but I'm not going to be 'Mr. Nanotech' the rest of my life." Which makes sense. You don't amass a résumé befitting the most interesting man in the world by being consistent. Rather, Brand has abandoned successful projects, radically revised his opinions, and broken with orthodoxies he helped create. He stopped regularly publishing the Whole Earth Catalog in 1972, the same year he wrote one of the first articles in a national magazine on computer hackers – "Spacewar," for 'Rolling Stone.' He co-founded the WELL (Whole Earth 'Lectronic Link), a primordial dial-up internet-service provider and influential online forum for Deadheads, techies, reporters, and often a compelling mix of Bay Area freethinkers. He organized the first Hackers Conference, in 1984, bringing together MIT computer geeks, 1970s-era hardware freaks, and a new clique of hardcore gamers, whom Brand recognized as part of the same creative continuum. It was at this conference that he coined the phrase "information wants to be free." Prophetically, he said it also "wants to be expensive." From 1974 to 1984, he edited another eclectic publication, CoEvolution Quarterly, which introduced ideas many of his admirers must have found unconventional, if not outright heretical: cybernetics, space colonies, ecogenetics, even the flat tax. Since 1988, he has helped run Global Business Network, a scenario-planning consultancy (think risk assessment, forecasting models, and something called "visioning") that brings the futurist outlook to Bechtel, General Electric, Siemens Westinghouse, the Pentagon – clients one certainly wouldn't associate with the Whole Earth Catalog. Then, in 2009, Brand published 'Whole Earth Discipline: An Ecopragmatist Manifesto,' in which he declared nuclear energy, genetically modified foods, and increased urbanization essential "green" solutions to global warming. Needless to say, some of those who considered Brand a fellow environmental traveler found these "solutions" troubling. Amory Lovins, chairman of the Rocky Mountain Institute and a longtime friend of Brand's, said the book's advocacy of nuclear energy ran contrary to "Stewart's reputation and prior contributions to clear thinking" and "can only worsen climate and security risks."

Still, I searched and found no trail of bitter ex-associates who felt betrayed or abandoned by Brand. He has an uncanny way of consoling those who don't see eye to eye with him. He wants his mind changed and is without ideology or ego. The open-source software activist Tim O'Reilly describes Brand as an "intellectual Renaissance man, interested in all aspects of human knowledge." Larry Brilliant, an epidemiologist who founded the WELL with Brand and later went on to run several companies and major philanthropic organizations (Brilliant also helped eradicate polio in India and spent time living on Wavy Gravy's commune, the Hog Farm), says, "Stewart's gift, his genius, is that he has given birth from his fertile, polymath mind to a dozen different cultural phenomena that have shaped our times."

The satirist Paul Krassner lived with Brand in the early 1970s, moving from New York to San Francisco to co-edit a supplement of the Catalog with Ken Kesey. Krassner could recall only one incident in which the roomies had any real tension, a conflict prompted by Krassner and his girlfriend "borrowing" Brand's bed. Not only did the woman in question turn out to have her period, but the two of them breakfasted on the sheets, leaving the bed, as Krassner put it, "bloody and granola-y." Brand was pissed when he returned home, but peace and understanding were restored through the use of a tool advertised in the Catalog: The two men brandished foam bats called "boffers" and harmlessly thrashed each other.

As Brand dries our REI coffee mugs with a Lycra headband he has been wearing around his neck, I ask him about the moments in his life when he felt he had a clear sense of the future. He does another one of his reflective pauses and then finally says, "An interesting question to ask is what predictions have I been wrong about in my lifetime." These would include, among others, Fuller domes, the geodesic shelters designed by futurist Buckminster Fuller, whose work inspired the first Whole Earth Catalog. "They leaked and made terrible homes," Brand says. The "no hope without dope" thing, he says with a laugh, seemed promising back when he was hanging with Ken Kesey and Jerry Garcia, but turned out to be a dead end. There was the Whole Earth Software Catalog, which was almost wholly obsolete by the time it reached publication. Brand predicted that he'd live to see space colonies and nuclear fusion (he remains hopeful about the latter). He opposed the adoption of the metric system. More recently, the Long Now Foundation launched something called Long Bets, an online venue where people can wager on the accuracy of opposing viewpoints. In 2008, Warren Buffett used the site to bet a group of hedge-fund traders $1 million that the S&P would outperform their picks over a 10-year period. Brand thought Long Bets would take off, becoming a locus for the big debates of our time. "I don't get it," he says, sounding still surprised. "The site is totally lame and half-assed."

After our hike, Brand takes me to Sausalito, where he lives on a refurbished tugboat with his wife of 28 years, Ryan Phelan. (Brand has a grown son from an earlier relationship.) He describes Phelan as a "serial entrepreneur," which he means as a term of ardent endearment. The two bought the 100-year-old boat, the Mirene, in 1982 for $8,000. It now has a fresh coat of black-and-white paint with shiny red trim and sits in Richardson Bay amid 400 other houseboats. A low-rider bicycle covered in shaggy fur is tied up on the dock. It's a relic from Burning Man, the annual gathering in the Nevada desert that Brand describes, accurately, as a grandchild of the experiments in community that he organized.

"Life on a boat is environmentally sound," Brand says. "In California, it better protects you from earthquakes, wildfires, and mudslides. It even will buffer you from global warming's rising tides."

The Whole Earth Catalog used to keep its offices just off the dock here, and Brand shows me the area where he and the staff played volleyball every day at noon. (The entire Googleplex/tech-start-up notion that a hard-driving workplace should also be a source of merrymaking and healthful recreation owes a debt to Brand as well.) When he lived across the bay, in Belvedere, he rowed to work each day. He now keeps two offices nearby, one in a cramped prefabricated building and another on a rickety fishing boat propped up on land. Farther down is a small industrial-design shop, where guys Brand has known since they were kids are building marine-radar systems and robotically navigated submarine vessels that map the ocean floor. At the Mexican diner a block away, where we eat lunch, Brand simply tells the owner, "I'll have the usual."

Brand served in the Army as an officer from 1960 to 1963. I'm initially puzzled by how early and often in our conversations Brand praises his time in the military, but I come to see how much this period in his life defines him. He credits the Army with teaching him how to judge character, how to accomplish goals. "I learned how to back the fuck off and let the 'sergeants' do their work," he says. Although in some respects a flower child, Brand never grew a beard or long hair, last dropped acid in 1969, calls Zen boring, and dismisses the New Left activists of his youth as all talk and no action – a failing Brand clearly cannot abide. In 'The Electric Kool-Aid Acid Test,' Tom Wolfe's book on the psychedelic peregrinations of Kesey and his hippie companions, Brand is identified as the "restrained, reflective wing of the Merry Pranksters." (Krassner describes his time rooming with Brand as "a New Age Odd Couple," with Brand as Felix.) It was Brand who organized the Merry Pranksters' famous Trips Festival, a music-and-light show attended by 10,000 people, many of whom saw their first (of many) Grateful Dead shows there.

Maybe most famously, during an LSD-induced vision in 1966, Brand wrote in his journal, "Why haven't we seen a photograph of the whole Earth yet?" The first space launch was more than a decade old, and Brand believed the image would transform how humans conceived of the planet. He began distributing buttons displaying his question – they quickly became popular in the Haight, in Oakland, and eventually at NASA. Photographs from space were released in 1968 and soon appeared on the covers of both the first Whole Earth Catalog and 'Life' magazine (and later on your Mac screen), providing just the jolt to environmental consciousness that Brand had envisioned. Two years later, more than 20 million Americans attended rallies for the inaugural Earth Day.

One night, I go with Brand and his wife to the Castro Theatre in San Francisco for one of the Long Now Foundation's seminars on long-term thinking. The speakers at these events can range wildly, everyone from Michael Pollan to Brian Eno, with many points in between. As the theater fills to capacity, Brand notes that Long Now doesn't attract only Silicon Valley folk. It draws in a younger, less established crowd as well. "The 10,000-year clock gives them a sense of – a belief in – a better future," he says.

I think about how the younger people in the audience perceive Brand, as he takes the stage that night. He is not cool in any conventional sense, nor is he slick in presentation or attire, like some Timothy Ferriss type. Nor does he possess the laid-back vibe of, say, Steve Jobs, with his faded Levi's and mock turtles. Brand has dressed that evening in a moisture-wicking, triple-stitched 5.11 tactical shirt with a half-dozen pockets, including ones hidden along the chest that are specifically marketed as just right for a small backup piece. Brand informs me that he has 10 of these shirts, presumably all in tan, gray, or pea green, the only colors I see him wearing. Two knives hang conspicuously from Brand's belt – not just a practical Swiss Army but also his "dress knife," an ornate specimen reserved for formal occasions. "If there's a rumble," a guy seated behind me remarks, "I'm sticking with him." A woman in her twenties, her hair emerging from a modish hat in several long braids, tells me Stewart Brand is one of the reasons she moved to the Bay Area. It's a statement one could have heard almost verbatim in San Francisco back in the 1960s, or really in any decade since. I mention Brand to a recent Reed College graduate at the seminar, and he suddenly dashes off, returning moments later holding a hardbound copy of his senior thesis, partly written about Brand, which he had stashed in the movie house's recesses. He thought about returning to San Antonio after college, he says, but realized he needed to be here, among people dedicated to the same dreams. "Brand showed us that technology wasn't a malevolent or necessarily a positive force," the Reed guy tells me. "Like Steve Jobs, he demonstrated that it's another tool in the toolbox."

Michael Phillips, a MasterCard company creator, helped Brand run the foundation that seeded out the earnings from the Whole Earth Catalog. "Underlying everything Stewart does is an optimism and experimentation," Phillips says. "He's always testing radical alternatives, believing that the best ideas will win out and lead to a better future."

Brand is still seeking new ways to bring people together, to shape what lies ahead. His latest venture: using genetics to re-create extinct species. There's the passenger pigeon for starters, the mammoth, the Tasmanian tiger. Brand says the technology to reconstitute these animals is already rushing forward, and he hopes to ensure that the process is carried out responsibly. The project is a suitable one for a person who apparently transcends time. All of us dinosaurs fossilized in our own pursuits – Stewart Brand will show us the way. He may even help undo a bit of the ecological havoc we've wreaked on the planet, never mind that some will consider it, as Brand puts it, "the ultimate trespass on the natural world."

"When you think and act long-term, you keep your options open for the future," he says. "You open up the past and the present."