Afonso II of Portugal (English: Alphonzo), or Affonso (Archaic Portuguese), Alfonso or Alphonso (Portuguese-Galician) or Alphonsus (Latin version), known as the Fat (Port. o Gordo), third king of Portugal, was born in Coimbra on April 23, 1185 and died on March 25, 1223 in the same city. He was the second but eldest surviving son of Sancho I of Portugal by his wife, Dulce of Barcelona, Princess of Aragon. Afonso succeeded his father in 1212.

As a king, Afonso II set a different approach of government. Hitherto, Sancho I his father and Afonso I his grandfather, were mostly concerned with military issues either against the neighbouring Castile or against the Moors in the south. Afonso did not pursue territory enlargement policies and managed to insure peace with Castile during his reign. Despite this, some towns, like Alcácer do Sal in 1217, were conquered from the Moors by the particular initiative of noblemen. This does not mean that he was a weak or somehow cowardly man. The first years of his reign were marked instead by internal disturbances between Afonso and his brothers and sisters. The king managed to keep security within Portuguese borders only by outlawing and exiling his kin.

Since military issues were not a government priority, Afonso established the state's administration and centralized power on himself. He designed the first set of Portuguese written laws. These were mainly concerned with private property, civil justice, and minting. Afonso also sent ambassadors to European kingdoms outside the Iberian Peninsula and began amiable commercial relations with most of them.

Other reforms included the always delicate matters with the pope. In order to get the independence of Portugal recognized by the popes, his grandfather, Afonso I, had to legislate an enormous amount of privileges to the Church. These eventually created a state within the state. With Portugal's position as a country firmly established, Afonso II endeavoured to weaken the power of the clergy and to apply a portion of the enormous revenues of the Catholic church to purposes of national utility. These actions led to a serious diplomatic conflict between the pope and Portugal. After being excommunicated for his audacities by Pope Honorius III, Afonso II promised to make amends to the church, but he died in 1223 before making any serious attempts to do so.

Afonso married Urraca, princess of Castile, daughter of Alfonso VIII, King of Castile, and Leonora of Aquitaine, in 1208.