Isabella I ( Spanish : Isabel) (1451–1504), queen of Castile and León, 1474–1504. In 1469 Isabella married Ferdinand of Aragon. When Ferdinand succeeded to the Aragonese crown in 1479, the pair became joint rulers of both realms. Their grandson, Charles I (Charles V of the Holy Roman Empire), was the first ruler of a united Spain.

Isabella was noted for her intelligence, determination, and piety. The European discovery of America by Christopher Columbus was made possible by her sponsorship; she even offered to pawn her jewels to finance the voyage. Isabella supported the war against the Moors, the expulsion of the Jews, and the introduction of the Inquisition to Castile. Ferdinand and Isabella were known as “the Catholic sovereigns.”