Isabella I, also called Isabella the Catholic, was Queen of Castile and León from 1474 until her death in 1504. She was also Queen of Aragon from 1479 until her death as the wife of King Ferdinand II. Reigning together over a dynastically unified Spain, Isabella and Ferdinand are known as the Catholic Monarchs.

Spanish or Castilian (castellano) is a Romance language of the Indo-European language family that evolved from the Vulgar Latin spoken on the Iberian Peninsula of Europe. Today, it is a global language with about 500 million native speakers, mainly in the Americas and Spain, and about 600 million when including second language speakers. Spanish is the official language of 20 countries, as well as one of the six official languages of the United Nations. Spanish is the world's second-most spoken native language after Mandarin Chinese; the world's fourth-most spoken language overall after English, Mandarin Chinese, and Hindustani (Hindi-Urdu); and the world's most widely spoken Romance language. The country with the largest population of native speakers is Mexico.