Crowned bust left, IOHANES REX // CASTELLE E LEGIONIS, Castle, B below. 17mm, 0.77 grams. Numista 145402; AB#566

John I of Castile (1358–1390) reigned from 1379 to 1390 as king of Castile and León, succeeding his father Henry II, the founder of the Trastámara dynasty. His reign was troubled by tensions with Portugal, including the Battle of Aljubarrota in 1385, where his attempt to claim the Portuguese crown ended in a crushing defeat that secured Portuguese independence. Internally, he faced noble unrest and challenges to royal authority, though he sought to strengthen ties with neighboring realms through diplomacy and dynastic marriages. John I died in a riding accident in 1390, leaving the throne to his young son Henry III.