Rodrigo Díaz lived a violently colourful life in eleventh-century Spain. By turns an ambitious military leader, exile and brutal mercenary, he served Christian kings, fought against Christian princes, massacred Muslims and eventually struck out on his own, carving out an independent principality.

But the man Rodrigo is long dead. El Cid lives on: a superhero; a quasi-saint; the 'spirit of Spain', according to military dictator Franco; and a champion of medieval Spanish multiculturalism.

Nora Berend uncovers how el Cid has been transformed across the centuries, confronting the gulf between truth and legend and examining how a military adventurer became a hero to people on opposite ends of the political spectrum. The story of the Cid forces us to confront what makes us human. What is it about this man that appeals to us? And why do we transform the most unsuitable people into heroes?