In the 1960s, Che Guevara's bearded face appeared on the walls of student bedsits more dependably than rising damp. The famous photograph of straggly hair and saintly eyes was taken in the Cuban capital of Havana in 1960, a year after the revolución. Even in death, Guevara had a sainted air. After CIA-trained militia had executed him in Bolivia in 1967, the nuns at the hospital where his corpse was displayed kept locks of his hair. The 39-year-old was thought to resemble Mantegna's Dead Christ.

Guevara's brand of revolutionary peasant struggle is virtually meaningless today. The population of Latin America is increasingly urban and Uncle Sam is less evidently imperialist. Yet Guevara's Robin Hood glamour continues to appeal. An Argentinian of noble Spanish ancestry, he was nicknamed Che (“mate”) after his comradely leadership. He was the only non-Cuban on board the Granma cruiser that ferried 82 revolutionary exiles, led by Fidel Castro, from Mexico to Cuba in 1956.

Guevara devoted more than 10 years of his brief life to Castro's cause. Yet, as Simon Reid-Henry argues in this absorbing account of their friendship, he was a very different revolutionary from Castro. While Castro was the paunchy epicure, Guevara was an ascetic soul who cared little for wine or dance. (His real passion was chess.) He had been Castro's left-hand man in the nationalist revolt that toppled the Cuban dictator Batista in 1959, and was subsequently appointed director of the Cuban national bank. In his combat fatigues and beret, however, Guevara was not born to be a banker. He set up Cuba's first labour camps, and supervised an estimated 550 executions in post-Batista Havana.

According to the author, Castro has kept quiet all these years about the nature of his friendship with Guevara. Really? His admiration for Che was evident in his autobiography, first published in Spain in 2006, and was amply documented in recent biographies of Guevara by Jon Lee Anderson and Jorge Castaneda. Reid-Henry offers a synthesis of these sources, tracing Guevara's political awakening to his student days in Buenos Aires, where he took a medical degree in 1953. Obsessed with finding a cure for his chronic asthma, he wanted to remedy the social injustices of Latin America - at first through preventive medicine, later through armed rebellion.

Unhappy with Fidel's reforms - too much paperwork - Guevara left Cuba in 1965 to champion revolutionary causes in Zaire and Bolivia. Reid-Henry dismisses the notion that Guevara went to fight in Bolivia of his own will. It was Fidel who sent Guevara (already the father of five children) to Bolivia in the spring of 1966. The decision led to the Argentinian's death during a half-baked guerrilla insurrection.

Were he alive today, Ernesto Guevara (de la Serna) would be approaching 80. He died with his boots on, caught in full stride as he would have wanted, leaving his compañero Castro bereft for the rest of his 39 years in power.

Fidel & Che by Simon Reid-Henry
Sceptre £20 pp467

Times Recommends

• The 100 Best Books of the Decade
• The Times picks the 50 best paperbacks of 2009
• The conversation: James Ellroy