AS a volunteer in the International Brigades that fought in Spain's civil war, the unidentified black soldier in the photograph was one of the first Americans to die fighting fascism. Now Spanish authorities want to put a name to him so they can present his picture to President Barack Obama when he visits Spain next year.

The black and white picture of the African-American volunteer forms part of an extraordinary collection of civil war photographs that was bought recently by the Spanish state.

“All we know is that he arrived with the Abraham Lincoln Brigade of American volunteers and that he died in the battle at Brunete [in July 1937],” said Sergi Centelles, whose father, Agusti, took the picture.

The soldier is one of more than 90 African-Americans who volunteered to defend Spain's elected Republican government from a 1936 rightwing military uprising that sparked a three-year civil war.

Germany's Adolf Hitler and Italy's Benito Mussolini sent troops to back the rebel army of future dictator General Francisco Franco. Leftwing and anti-fascist volunteers from around the world joined Russians sent by Stalin to help defend the Republic. Obama defended the concept of waging a “just war” in his Nobel peace prize speech this month.

The New York-based Abraham Lincoln Brigades Association and New York University's Tamiment library have scoured their civil war archives to see if they could identify the man in the photograph, which was probably taken in Feb 1937. Two possible candidates have emerged Milton Herndon, whose brother Angelo won a famous supreme court case against a sentence for “incitement to insurrection”, and aviator Paul Williams.

“It is one of eight or nine photographs my father took of the Americans marching through Barcelona,” said Agusti Centelles.

The photograph remained hidden for four decades after Agusti Centelles, known as the “Spanish Robert Capa”, fled Spain as Franco's forces looked set to win the civil war in 1939.

“My father took his photographs with him in a suitcase because he was scared they would be used to identify people and carry out reprisals,” said Sergi Centelles.

The photographer used the suitcase as a pillow in a French refugee camp to prevent it from being stolen. He later moved in with a French family in Carcassonne, in southern France, but had to flee again after the Second World War broke out and the occupying Germans heard that he was using his camera to take photographs for false passports.

— The Guardian, London