House of Aviz
The Portuguese Royal House of Braganza began with John IV. The dukes of the House of Braganza were a branch of the House of Aviz created by King Afonso V for his half-uncle Afonso, 8th Count of Barcelos, illegitimate son of John I, first monarch of the House of Aviz. The Braganzas soon became one of the most powerful families of the kingdom and for the next decades would inter-marry with the main line of the Portuguese royal family. In 1565, John, 6th Duke of Braganza married Princess Catherine, granddaughter of King Manuel I. This connection with the Royal Family proved determinant in the rise of the House of Braganza to a Royal House. Catherine was one of the strongest claimants of the throne during the succession crisis of 1580 but lost the struggle to her cousin Philip II of Spain. Eventually Catherine's grandson became John IV of Portugal as he was held to be the legitimate heir.