Harry Villegas, Che Guevara’s right-hand man and bodyguard best-known by his nom de guerre Pombo, was one of the last people to see Guevara alive in Bolivia in 1967. The two had fought shoulder-to-shoulder during Fidel Castro’s Cuban revolution in the late 1950s and had driven victoriously into Havana on the first military truckload of revolutionaries on Jan. 2, 1959 — six days before Castro, slowed by cheering crowds, arrived in the capital.

“I’d never seen such a big city before,” Mr. Villegas, who died Dec. 29 at 81, recalled in his memoir, “Pombo.” “I’d never been out of my own countryside.”

A descendant of African slaves, Mr. Villegas went on to fight alongside Guevara in Africa in 1965 — in what was then known as the Congo (now the Democratic Republic of the Congo) — as Castro sought to promote communist revolution worldwide.

Cuba’s African adventure failed. “We didn’t understand the psychology of the Africans,” Mr. Villegas recalled. He then followed the man he called Tatu — Guevara — to the jungles and mountains of Bolivia.

Surrounded by the U.S.-backed Bolivian army, Guevara, already wounded in a firefight, told Mr. Villegas and two other Cuban guerrillas to try to save themselves by slipping through the Bolivian cordon. They did and, with help of leftist sympathizers, made it back to Cuba six months later via a circuitous, clandestine route including Chile, Easter Island in the Pacific, Tahiti, Ethi­o­pia, France and Russia.

Guevara was captured in a mountain ravine on Oct. 8, 1967, taken to a tiny village schoolhouse at La Higuiera, southern Bolivia, and interrogated by Bolivian army officers and a Cuban American CIA agent, Félix Rodríguez, who had been in Bolivia for three months, wearing a Bolivian army uniform, tracking the guerrilla leader’s movements and advising the Bolivians.

The following day, after Rodríguez had taken the last photographs of the now ragged, long-haired, thick-bearded Guevara alive so that the CIA could confirm his identity, the guerrilla icon was executed by Bolivian army sergeant Mario Terán with two bursts of his semiautomatic rifle. The CIA man had told Terán to shoot him “from the neck down” to make it look as though he had died in combat.

In his memoir, Mr. Villegas wrote that Guevara could have escaped the army encirclement but was never inclined to retreat.

When he last saw Guevara, he described his commandant as exhausted, wounded and bootless — but unbowed.

“There was never a single moment when Che lost control, enthusiasm or complete confidence in victory,” he wrote. “The day he was captured, he was analyzing how to get out of the zone and find another part of Bolivian territory to continue the struggle.”

Harry Antonio Villegas Tamayo was born March 10, 1938, according to the Cuban state media and military, although some Western reports put his birth in 1940. His birthplace was Yara, a southeastern Cuban village where the indigenous Taíno chief Hatuey was burned at the stake in 1512 after revolting against the Spanish conquistadors.

Mr. Villegas’s father was a carpenter but also a student of Cuban history. His mother was a descendant of African slaves. He attended primary school in Yara before continuing his schooling in Manzanillo, becoming a Boy Scout and a useful first baseman for a local team.

News soon arrived that an exiled Cuban, Castro, had come back to the island clandestinely to overthrow the island’s U.S.-backed military dictator, Fulgencio Batista.

Still a teenager, Mr. Villegas became the Argentine-born Guevara’s lieutenant soon after Guevara, Castro and 80 other poorly armed, seasick revolutionaries arrived in Cuba on a rickety boat named the Granma from Mexico in October 1956. The young Mr. Villegas was one of the first to link up with them on the island.

Guevara trained Mr. Villegas — in weapons, communism, poetry and chess — at Minas del Frío, a bitterly cold sugar- and coffee-growing village in the Sierra Maestra of southeastern Cuba. Reachable only by foot or mule, it was a perfect fortress against Batista’s army, although Mr. Villegas recalled regular machine-gun fire from below and bombings from above by Batista’s air force.

Mr. Villegas would go on to fight alongside Guevara, including at the key Battle of Santa Clara after Christmas 1958. When the dictator Batista realized Santa Clara had fallen, he fled Havana in the wee hours of New Year’s Day 1959, reportedly with $300 million cash in his briefcase and more than twice that much already in banks overseas.

Guevara and Mr. Villegas rumbled into the city as heroes the following day and, that June, Mr. Villegas was best man at Guevara’s wedding to fellow guerrilla Aleida March. Guevara returned the favor when Mr. Villegas married Cristina Campuzano in 1964. They had a son, Harry Jr.

Cuban news media, which reported Mr. Villegas’s death in Havana and said the cause was multiple organ failure, did not release details about survivors.

As for the Congo mission, Mr. Villegas recalled the hardships, which Guevara, although asthmatic, seemed able to ignore. They clandestinely crossed the mighty Lake Tanganyika several times in small motor launches to and from their 2,000-meter-altitude guerrilla base.

It was there that Mr. Villegas got the Swahili nickname Pombo, meaning something like “vegetable leaf.” He used to carry a 75-pound backpack up and down those slopes, as well as his weapons, receiving seeing little sympathy from his Argentine commander, whose backpack included mostly books, poetry, a chess set and photos of his family.

Guevara’s disciplinarianism and blinkered devotion to revolution was often on display. According to the 1997 biography “Che Guevara: A Revolutionary Life,” by American journalist Jon Lee Anderson, Guevara got upset at his friend Pombo, at the time his bodyguard in Havana after the revolution.

Quoting a female witness, Anderson wrote: “Che made Harry Villegas, his favorite, strip off his clothes before he was locked in a closet as punishment for some misdemeanor. Che’s mother was visiting, and she yelled at him, telling him to be more lenient. He told her to keep out of it, that he knew what he was doing.”

It was while crossing Lake Tanganyika after the African venture had failed that Guevara told Mr. Villegas he wanted to create a communist revolution in his native Argentina. But Guevara ruled Mr. Villegas out of this mission based on a desire to remain inconspicuous, explaining via another of his key men that it was “because he’s black and where you’re going there are no blacks,” according to Anderson’s biography.

Guevara never got traction on the Argentina mission, so he opted to focus on Bolivia. Mr. Villegas was back on the team and would remain by his commandant’s side until the end.

After the Cuban revolution, Castro put Guevara in charge of the Department of Industrialization, focused on agrarian reform. The latter gave Mr. Villegas a job in the department while keeping him on as his bodyguard in full knowledge that he, Guevara and Castro were prime targets for the CIA.

Mr. Villegas lived in an annex of Guevara’s house in Havana and was always by his side elsewhere. After Guevara’s death, Mr. Villegas stayed in the Cuban army, rising to brigadier general, and served as a Cuban military adviser in Angola and Nicaragua. He was decorated as a national hero in Cuba.

Once asked whether Guevara ever talked of death, Mr. Villegas responded: “Never. He couldn’t conceive of it. It was hypothetical. For him, in war, there were two baskets — win or lose. Che died as he lived: full of optimism.”