Sebastian (Portuguese: Sebastião I Portuguese pronunciation: [s?b??'ti.?~w~]; 20 January 1554 – 4 August 1578) 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 (presumably killed in action) in the battle of Alcácer Quibir.
Sebastian I is often referred to as The Desired (Portuguese: o Desejado) or The Asleep (Portuguese: o Adormecido), 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 in the mountain legend as Portuguese tradition states his return, in a foggy dawn, on Portugal's greatest hour of need.