Sebastianism in Portuguese and Brazilian mythology and culture is the belief that King Sebastian of Portugal will return to save Portugal. The belief gained momentum after an interpretation by priest António Vieira of Daniel 2 and the Book of Revelation that foreshowed a Portuguese Fifth Empire. In Brazil the most important manifestation of Sebastianism took place in the context of the Proclamation of the Republic, when movements emerged that defended a return to the monarchy. It is categorised as an example of the King in the mountain folk motif, typified by people waiting for a hero to return to save them. The Portuguese author Fernando Pessoa wrote about such an hero in his epic Mensagem (The Message).
King Sebastian of Portugal (January 20, 1554 - August 4, 1578), grandson of John III, who became heir to the throne due to the death of his father, João, Crown Prince of Portugal in 1554 two weeks before his birth, and who succeeded to the throne three years later. This period saw continued Portuguese colonial expansion in Africa, Asia and Brazil. The young King grew up under the guidance of the Jesuits. Luís de Camões dedicated the Lusiads to King Sebastian.
Almost immediately after coming of age, Sebastian began plans for a great crusade against the Moroccans of Fez. The Portuguese crossed into Morocco in 1578 and, against the advice of his commanders, Sebastian marched deep inland. At Ksar El Kebir (Field of the Three Kings) the Portuguese were routed by Ahmed Mohammed of Fez, and Sebastian was almost certainly killed in battle or subsequently executed. But for the Portuguese people, he had just disappeared and would return home one day, to such an extent that, in 1640, King John IV of Portugal had to swear to yield his throne to Sebastian, in case Sebastian (who would have been 86 years old) were to return.