King Ferdinand III of Castile was a significant monarch in the 13th century, known for his role in the Reconquista, the effort to reclaim the Iberian Peninsula from Muslim rule. He became king of Castile in 1217 and later added the crown of León in 1230. His reign was marked by military successes, including the capture of Seville in 1248. Ferdinand III was also recognized for his administrative reforms and efforts to promote peace and justice within his kingdom. He was canonized as a saint by the Catholic Church in 1671, reflecting his lasting legacy in Spanish history.