Sebastião I of Portugal was the King of Portugal from 1557 until his death in 1578. He became king at a young age, following the death of his grandfather, King John III. Sebastião was known for his ambitious plans to expand Portuguese territories, particularly in North Africa. His reign ended tragically when he led a disastrous military campaign against the Moorish forces at the Battle of Alcácer Quibir. Sebastião disappeared during the battle, leading to speculation about his fate. His disappearance created a succession crisis, ultimately leading to the Iberian Union under Philip II of Spain.