Sebastian was King of Portugal from 11 June 1557 to 4 August 1578 and the penultimate Portuguese monarch of the House of Aviz.
He was the son of João Manuel, Prince of Portugal, and his wife, Joanna of Austria. He was the grandson of King John III of Portugal and Holy Roman Emperor Charles V. He disappeared in the battle of Alcácer Quibir, against the Saadians of Morocco. Sebastian I is often referred to as The Desired or The Asleep, as the Portuguese people longed for his return to end the decline of Portugal that began after his death. He is considered to be the Portuguese example of the King asleep in mountain legend as Portuguese tradition states his return, in a foggy dawn, on Portugal's greatest hour of need.