King Henry I of Portugal was a monarch who ruled from 1578 to 1580. He was the son of King John III of Portugal and Catherine of Austria. His reign was marked by a lack of strong leadership and political instability, leading to a succession crisis after his death. Henry was known for his devout Catholic faith and his efforts to maintain Portugal's influence in the Age of Discovery. However, his inability to produce an heir resulted in a power struggle, ultimately leading to the Portuguese succession crisis and the eventual annexation of Portugal by Spain.