“We’ve only captured a very small fraction of the potential market,” he said, sounding more entrepreneurial than philosophic. “Stoicism is a philosophy designed for the masses, and if it has to be simplified a bit to reach the masses, so be it.”

If Stoicism is becoming trendy, you can credit, or blame, Mr. Holiday. Through his popular books, lectures and viral articles, he translates Stoicism, which had counted emperors and statesmen among its adherents during antiquity, into pithy catchphrases and digestible anecdotes for ambitious, 21st-century life hackers. He boils down the philosophy’s central tenets to inspirational tales from successful people’s lives (Steve Jobs? Bill Bradley? Model stoics!) and recasts its ancient maxims about the pitfalls of pride into breathless clickbait (“25 Ways to Kill the Toxic Ego That Will Ruin Your Life”). On Twitter, he blasts out uplifting quotations from ancient philosophers like Cleanthes, Diogenes of Sinope, Plato and Zeno to his more than 80,000 followers.

His 2014 book, “The Obstacle Is the Way: The Timeless Art of Turning Trials Into Triumph,” which draws on the teachings of the Roman emperor Marcus Aurelius and other Stoics, sold more than 230,000 copies in the United States and has been translated into 19 languages. It has drawn high-profile acolytes, including professional athletes, federal judges, Hollywood celebrities and venture capitalists. Arnold Schwarzenegger is a fan. So is LL Cool J, who sent Mr. Holiday a message on Twitter after reading “Obstacle.”

Mr. Holiday, 29, is an unlikely poster boy for Stoicism. He is a college dropout and a former public-relations strategist for American Apparel, where he did damage control during the company’s ouster of its controversial founder, Dov Charney. He runs his own marketing firm, Brass Check, and has written boastfully of the depraved publicity tactics he deployed on behalf of his clients, including forging and leaking documents, creating fake Twitter accounts and buying web traffic for blog posts he generated. He hatched a viral publicity stunt for the unabashedly lecherous author Tucker Max (“I Hope They Serve Beer in Hell”), which involved vandalizing billboards for a movie based on the book and emailing photos of the defaced ads to blogs in an attempt to stir up a feminist boycott of the movie on college campuses.

Image Mr. Holiday’s 2014 book, “The Obstacle Is the Way: The Timeless Art of Turning Trials Into Triumph,” draws on the teachings of the Roman emperor Marcus Aurelius, pictured, and other Stoics. Credit... Hulton Archive/Getty Images

Now, he is harnessing his considerable marketing prowess to sell Stoicism. He is like a snake-oil salesman who swears he has abandoned snake oil, but not the highly effective sales tactics.