Alfonso XI (August 13 , 1311 – March 26/27, 1350) is the king of Castile, León and Galicia.

He is the son of Ferdinand IV of Castile and his wife Constance of Portugal.

Upon his father's death in 1312, several disputes ensue over who will hold regency, which are resolved in 1313.

Once Alfonso is declared adult in 1325, he begin a reigns that will serve to strengthen royal power.

His achievements include solving the problems of the Gibraltar Strait and the conquest of Algeciras.