Dan Wieden, co-founder of the Portland, Ore.-based advertising agency Wieden+Kennedy who was personally responsible for the “Just Do It” slogan in 1988 that helped catapult Nike into a multibillion-dollar sports apparel company, died Sept. 30 at his home in Portland. He was 77.

The company announced the death without specifying a cause.

The three-word, eight-letter tagline, along with Nike’s swoosh logo is considered one of the most successful and recognizable in the history of advertising, and it came about as the shoe company was struggling against formidable competitors such as Reebok and Adidas, whose ads capitalized on the youth-oriented fitness craze of the 1980s.

Mr. Wieden, once an aspiring playwright who grudgingly entered the ad business, had worked for large firms before hanging his own shingle with business partner David Kennedy after reading a book titled “How to Start an Advertising Agency.”

The founding was on April 1, 1982 – April Fools’ Day – marking an irreverent style that became their hallmark. They kept beer on tap at their offices and also had a full-scale basketball court on the premises, among other amenities designed to make work feel like play. A reporter from the New York Times described the building as “a temple of outrageousness.” One of their party guests, Ken Kesey, author of the novel “One Flew Over the Cuckoo’s Nest,” reportedly told the founders, “You could teach the Hells Angels how to party!”

Even daring to launch in Portland was a gamble, with the major ad agencies based in New York, Chicago or Los Angeles. “No one in their right mind would start an international agency in Portland, Oregon,” Mr. Wieden reflected years later.

Nike, a small but growing company based in nearby Beaverton, was their first major client. Although Mr. Wieden was hardly a fitness enthusiast – he once tried to jog in a pair of jeans, only to chafe his crotch, he told the Portland Oregonian – he shared a rebellious spirit with Nike founder Phil Knight, who had introduced himself to the duo with the declaration, “I’m Phil Knight, and I hate advertising.”

It took years for Mr. Wieden and Kennedy to gain a foothold in the industry, as Nike also gave its business to the giant Chiat/Day firm to handle its advertising for the 1984 Summer Olympic Games. But Wieden+Kennedy’s ad the next year – featuring Lou Reed of the Velvet Underground riding a Honda scooter through New York City to the backtrack of his 1972 hit “Walk on the Wild Side,” impressed Knight with its moody intensity.

Although scooter sales did not experience a major uptick, Knight began investing vastly more in the upstart advertising company. Mr. Wieden and his creative team had made ads for Nike featuring shoes for different types of sports and athletes, but they felt they needed a unifying slogan to bind them all together. Mr. Wieden, who was always quick to credit teamwork for many successes, said he came up with “Just Do It” largely on his own.

The idea was inspired by an atypical source: the final words of convicted murder Gary Gilmore, whose 1977 killing by firing squad in a Utah prison was the first execution in the United States after a 10‐year moratorium on the death penalty.

Mr. Wieden said he read Norman Mailer’s acclaimed 1979 book about Gilmore, “The Executioner’s Song,” and remembered that the death-row prisoner was asked if he had any last words before being shot. The brazen cheekiness of the response – “Let’s do it!” – stuck with him. Scribbling on a notebook, he wrote, at first “Do It,” later adding the “Just.”

The tagline first appeared on a July 1988, TV ad, directed by Kennedy and featuring an 80-year-old man, Walt Stack, who ran 17 miles every morning including over San Francisco’s Golden Gate Bridge – aspiring to sell a shoe that could meet the need of everyone regardless of age or fitness level.

“Just do it” quickly entered the cultural zeitgeist as a catchphrase meant to represent living life on your own terms, daring to take chances on and off a playing field. “You wouldn’t believe the response,” Liz Dolan, director of Nike public relations, told The Washington Post in 1989. “We’ve gotten zillions of letters from consumers who’ve told us it’s made them change their lives. One woman left her husband.”

Over the next several decades, Nike sales boomed 1,000 percent, with the “Just Do It” ads featuring prominent athletes such as Michael Jordan and Colin Kaepernick. Wieden+Kennedy was also behind the clever “Bo Knows” commercials for Nike’s cross-training shoes featuring athlete Bo Jackson and blues-rock guitarist Bo Diddley.

Although Nike remained its biggest client, Wieden+Kennedy also did advertising work for McDonalds, Ford, Coca-Cola, Samsung, ESPN and Uniqlo, among other major firms. The agency, now employing 1,500 people in eight offices worldwide, won multiple awards, including Global Agency of the Year four times from the trade publication Adweek. Mr. Wieden never formally retired but remained active as a trustee, often visiting the Portland headquarters to give encouragement and guidance to new staff.

“The reason it lasted so long was that he didn’t build an ad agency, he built a culture,” senior Wieden+Kennedy executive Karl Lieberman told the Oregonian. “Curious, driven, welcoming and lacking deference, . . . it’s a place that in a lot of ways reflects him.”

Veteran British advertising executive Alfredo Marcantonio wrote in an email: “In the sixties, Doyle Dane Bernbach and its fellow New York hotshots ruled the world so far as creative advertising was concerned. They so inspired the likes of London’s Collett Dickenson Pearce that the center of creative excellence crossed the Atlantic. It was Dan Wieden in Portland and also the late Pat Fallon in Minneapolis, far from Madison Avenue, who powered the U.S. to again vie for the international creative crown.

“He was a warm and gentle character, a complete contrast to the top dogs that he spent his career competing against,” Marcantonio added of Mr. Wieden. “No flamboyance, no flannel, no fuss. He just did it.”

Dan Gordon Wieden was born in Portland on March 6, 1945. His father worked his way up to the presidency of Joseph R. Gerber Advertising, one of the region’s biggest firms.

He graduating from the University of Oregon in 1967 with a bachelor’s degree in journalism. The previous year, he had married fellow student Bonnie Scott and soon began a fitful early career as floor manager for a local TV station and writing marketing copy for the forest‐products company Georgia-Pacific Corp. He said he was fired from the latter because he could barely contain his boredom. He devoted his spare time to studying literature and theater, at one point fancying himself as a budding playwright.

For years, he tried to avoid following in his father’s footsteps, seeing advertising as too conventional a path. But eventually, seeking greater financial security to support his growing family, he joined McCann-Erickson, the biggest ad firm in Portland, and partnered with like-minded colleague Kennedy, who similarly considered himself an outsider in a world of slick or button-down admen. “It was a perfect match of subversives,” the Oregonian wrote: “Wieden, the high-strung, jabbering, radical writer, and Kennedy, the taciturn, philosophical artist.”

Or as Kennedy put it to the New York Times: “Dan had four kids and lived in the country, and I had five kids and wanted to live in the country.”

Both left around 1980 for the William Cain Agency, where Mr. Wieden said he found himself dreading his work for yet another lumber company in the Pacific Northwest. But one client, Nike, fascinated them. Mr. Wieden and Kennedy jumped at the challenge to build a brand for the sports-shoe company lagging far behind its competitors. They quit Cain in 1982 to start their own firm, luring Nike as their sole client.

It has remained an independent agency ever since, despite the multiple takeovers of smaller agencies by international conglomerates in recent years, and is now run by a trust – suggested by Mr. Wieden – to ensure its independence. (Kennedy died in October 2021, at 82.)

Mr. Wieden’s first wife died in 2008. In 2012, he married Priscilla Bernard. She survives, along with four children from his first marriage; three stepchildren; a brother; a sister; and 12 grandchildren.

In the London-based magazine Creative Review, Mr. Wieden wrote this advice for creative teams: “Look, if you are driving for excellence, let me suggest you tell your left brain to take a break now and then. And give your right brain permission to let all hell break loose. I am not kidding. . . . You have to allow disorder and . . . foster a relationship with anxiety. With unpredictability. . . . The goal is not to march forward in lock-step harmony. . . . Excellence is not a formula, excellence is the grand experiment.

“It ain’t mathematics,” he added. “It’s jazz.”