Larry Harvey and Burning Man co-founder Marian Goodell in 1998, near Baker Beach in San Francisco. (Eric Risberg/AP)

Larry Harvey, a San Francisco landscape gardener who built an oversized human effigy, doused it with gasoline and ignited a countercultural phenomenon — the playfully anarchic, wildly imaginative art festival known as Burning Man — died April 28 at a hospital in San Francisco. He was 70.

The cause was complications of a stroke he suffered three weeks earlier, said his brother, Stewart Harvey.

Mr. Harvey was not the sole founder of Burning Man, but for more than three decades he was its singular creative force, guiding it from a whimsical celebration near the Golden Gate Bridge to an annual gathering in northern Nevada where 70,000 “Burners” create a scruffy frontier town with sculptures, art installations and an enormous burning effigy.

“The Burning Man is Disneyland in reverse . . . Woodstock turned inside out,” Mr. Harvey told the San Francisco Chronicle in 1996. “It is anything you want it to be.”

A onetime hippie vagabond, Mr. Harvey formed the seeds of Burning Man in 1986, after settling in San Francisco’s Haight-Ashbury district and mingling with a group of intellectually inclined tradesmen whom he dubbed the Latte Carpenters.

The “Man” burns on the Black Rock Desert at Burning Man in 2013. (Andy Barron/AP)

“It began as an impulse of an afternoon,” Mr. Harvey said on “Charlie Rose.” “I called a friend and I said, ‘Let’s burn a man.’ He said, ‘What? Would you repeat that statement?’ ”

Mr. Harvey and his friend, Jerry James, constructed an 8-foot effigy of recycled lumber and set it ablaze on Baker Beach, in the shadow of the Presidio of San Francisco military installation. By one account, Mr. Harvey had been inspired by “The Wicker Man,” a horror movie about a cult of Celtic pagans who build a towering wicker effigy; by another, he was motivated by a fellow San Francisco hippie, Mary Grauberger, who held arts-focused bonfires of her own.

Regardless, the effect of the fire was immediate and extraordinary. “It was like a second sun brought down to this earth,” Mr. Harvey later said. “Because at the moment it was lit, everybody on that beach, north and south, came running.”

With the help of artist-builders such as Michael Mikel and John Law, Mr. Harvey turned the bonfire into an annual celebration of the Summer Solstice before moving the festival to Nevada’s federally owned Black Rock Desert in 1990.

Attendance at the week-long event doubled each year in the early ’90s, swelling from several hundred people to several thousand.

The Man grew as well, from 40 feet in 1990 to 105 feet in 2014, and was joined by constructions that included drivable “art cars” and elaborate wooden temples by sculptor David Best. Additional structures were built according to annual themes, selected in part by Mr. Harvey, such as Hell (which featured a “McSatan” burger stand) and da Vinci’s Workshop (highlighted by a 70-foot-tall Vitruvian Man).

Mr. Harvey was known by many as “the man in the hat,” for the pearl gray Stetson that he invariably wore at Burning Man — an homage, he said, to his father, a Nebraskan who moved to Oregon during the Depression and preached a kind of cowboy code of honesty, simplicity and hard work.

The younger Harvey espoused a similar ethos, devising a set of “10 Principles” that emphasize “radical inclusion,” self-reliance, decommodification, self-expression and civic responsibility within the Burning Man community.

“It sounds like a conversion experience, you know, in religious terms,” Mr. Harvey said on “Charlie Rose,” recounting the “transcendent” experience described by many Burners. “So when they say we’re a cult, we reply that it’s a self-service cult, you wash your own brain.”

In 1996, a motorcyclist died at the event after colliding with a van, and several participants were wounded when a car drove through a tent. The incidents led some Burners to suggest that the event disband, or at least continue at a significantly reduced size.

Instead, Mr. Harvey helped modernize the festival, instituting reforms such as a street grid and address system that applied a semblance of order to the community. Firearms were regulated and then banned, after Burners reported that bullets were whizzing past tents. A security force was established to resolve disputes and rescue participants who were lost in the desert.

The changes were not universally appreciated, with one satirical song observing that “Burning Man, Burning Man, used to be so cool, before they went and [messed] it up with all these stupid rules.” In Mr. Harvey’s view, however, the new rules were a paradoxical necessity for a community that was founded on a belief in political and artistic freedom.

“A lot of people think it just ‘happens,’ and we just supply the porta-potties,” he told The Washington Post in 2012. “The irony is, we went to the desert to do something that was quite unworldly, and in order to survive and persist and realize our potential out there, we’ve had to get very worldly — it’s been a crash course.”

Larry Dean Harvey was born in Portland, Ore., on Jan. 11, 1948, and adopted by a family in Parkrose, a farming community that was later annexed by Portland. His father was a carpenter who developed a heart condition, leading Mr. Harvey’s mother to support the family as a cafeteria cook for the local school system.

Mr. Harvey “felt isolated and trapped” in their neighborhood, his brother said. There were few children his age, so as a young man Mr. Harvey immersed himself in books, devouring the works of Freud and William James.

He served briefly in the Army after graduating high school and attended Portland State College before dropping out to travel the country and, in 1974, settle in San Francisco.

His marriage to Patricia Johnson ended in divorce. In addition to his brother, survivors include a son, Tristan Harvey of San Francisco.

Mr. Harvey and Mikel suffered a falling out with Law, their co-founder, who left the organization after its calamitous 1996 iteration and later sued to have its trademark placed in the public domain. Mr. Harvey and others argued that the trademark helped prevent the Burning Man name from being co-opted by commercial interests, and settled out of court.

In 2013, Mr. Harvey oversaw the transfer of Burning Man’s organization from private ownership through Black Rock City LLC to the nonprofit Burning Man Project, where he held the title of chief philosophical officer.

“Larry did not believe in any sort of existence after death,” his friend and fellow Burning Man organizer Stuart Mangrum wrote in a post on the organization’s website. “Now that he’s gone, let’s take the liberty of contradicting him, and keep his memory alive in our hearts, our thoughts, and our actions. As he would have wished it, let us always Burn the Man.”