Lionel Martin, an American (and educated at a libertarian 'modern school', I think Stelton), moved to Cuba at the beginning of the 1960s as a sympathiser of the new government and got to know Fidel Castro, Che Guevara and other key figures in the Cuban revolution. There's a passing reference about his initial move to Cuba here.
These photos of Lionel shown here - he's the one with glasses and a beard and a lick of hair over his forehead - dates from 1975 when the American broadcaster Barbara Walters met Castro. It's not clear whether he was present as part of Castro's entourage, or perhaps more likely as a translator. It seems that on this occasion Walters was part of a group of American journalists visiting Cuba and given access to Castro. Two years later, Walters returned and did a celebrated one-on-one TV interview with the Cuban leader.
Martin wrote a book about Fidel Castro's political journey (The Early Fidel: roots of Castro's Communism, published by Lyle Stuart in 1978). He worked as a journalist in Havana, for the BBC and other outlets. I recorded this interview in Havana in July 1992, and it covers his memories of Castro and Guevara and his take on their political outlook and embrace of communism.
The interview was recorded for the programme about Cuba in the radio series What's Left of Communism? - there's a link below to the YouTube version of the programme.
Since posting this interview, I've learnt that Lionel Martin died in Havana in June 2019 aged 92. He had been unwell for some years before his death.