What was the name of the Spanish king who sponsored Columbus's voyages?

The Spanish king who sponsored Christopher Columbus’s voyages was Ferdinand II of Aragon.

Ferdinand ruled jointly with Isabella I of Castile, and the pair are known collectively as the Catholic Monarchs. Their support was formalized in the Capitulations of Santa Fe, signed on 17 April 1492, which authorized Columbus’s expedition and promised him titles and a share of the revenues from lands he claimed for the Crown.

The monarchs had initially hesitated because advisers considered Columbus’s estimate of the distance to Asia unrealistically low. After the conquest of Granada in January 1492, Ferdinand helped keep negotiations alive. Isabella ultimately approved the venture, while royal officials and the Crown arranged the expedition’s resources.

The first voyage began in August 1492, and Columbus returned in 1493. Ferdinand and Isabella later supported additional voyages, although their relationship with Columbus deteriorated as complaints arose about his administration in the Caribbean. Thus, Isabella was also a sponsor, but the question’s specifically male royal answer is Ferdinand II.