Korda, who died in 2001, Mr. Casey writes, would not be able to collect royalties on his wildly ubiquitous image until 1997, when the Castro government signed the Berne Convention for the Protection of Literary and Artistic Works, an international copyright treaty.

Image A truck advertising the Che soft drink in Vallegrande, Bolivia. Credit... Josefina Tommasi

Although Korda’s original photograph was not widely distributed for years, Mr. Casey says, Fidel Castro began using the image as a branding symbol for Cuba in 1967, months before Che’s death. It was a clever marketing plan on Mr. Castro’s part: Che’s denunciations of the Soviet Union made him popular among “thinkers and artists of the Western European left, many of whom had lost faith in the Soviet Union,” while his condemnation of imperialism “sat well with young radical students in the United States and Europe, who were impatient for societal change and for whom the very word revolution was inspiring.”

After Che was killed in Bolivia in October 1967 at 39, at the end of a disastrous guerrilla campaign, his fame and popularity  as a martyr now  spread even more rapidly around the world: red and black posters based on Korda’s photograph became symbols of the resistance movement during the 1968 student protests in Paris, and they surfaced, too, in America, where the revolutionary was embraced by both the Black Power movement and by hippies and antiwar activists.

In its May 17, 1968, issue, Time magazine observed that the Che legend had given “rise to a cult of almost religious hero worship among radical intellectuals, workers and students”: there were “Guevara-style beards” and berets in Italy, the magazine reported, and “handkerchiefs, sweatshirts and blouses decorated with his shaggy countenance” in “half a dozen countries”  all making for “a new source of profits for composers, poster makers and book publishers.” It was an article that could have easily run some four decades later, on the occasion of the 40th anniversary of Che’s death.

Image Michael Casey Credit... Josefina Tomassi

Clearly, it’s not what Che Guevara had in mind when he declared that “the revolutionary idea should be diffused by means of appropriate media to the greatest depth possible,” but in becoming one of the world’s most iconic brand names, Che has achieved an immortality that even exceeds the predictions of the stranger he meets at the end of his “Motorcycle Diaries,” who tells him “the spirit of the beehive speaks through your mouth and motivates your actions.”