Short answers, pulled from the story.
The Crown of Castile formed in 1230, when Ferdinand III united the Kingdom of Castile, which he had inherited from his mother in 1217, with the Kingdom of León, inherited from his father. The two kingdoms' parliaments merged into a single Cortes only decades later.
The Crown of Castile entered a personal union with the Crown of Aragon in 1479, after Isabella I and Ferdinand II, who had married in secret in October 1469, both came to power in their respective kingdoms. The two crowns remained administratively separate, sharing only the Inquisition as a common institution.
In 1492 Christopher Columbus's voyage claimed newly found lands in the Americas for the Crown of Castile, beginning its New World conquests. Castile went on to conquer the Aztec Empire and the Inca Empire, extend rule into New Granada, reach the Pacific Ocean, and take the Philippines, becoming a global empire in the 16th century.
The Catholic Monarchs pressed for religious uniformity, ordering in 1492 that any Jews who refused to convert to Catholicism would be expelled, and an estimated 50,000 to 70,000 people left Castile as a result. From 1502 onward, the same conversion pressure was extended to the Muslim population.
The Crown of Castile lost its separate existence after Philip of Bourbon won the War of the Spanish Succession in the early 18th century and imposed unification policies on the Crown of Aragon. The Nueva Planta decrees never formally dissolved the Crown of Castile, but the merged country came to be called Spain by both contemporaries and historians.
Alfonso X made Castilian the official language of the Crown of Castile in the 13th century, replacing Latin in public documents and legal translations. Because of Castilian's importance across the lands the Spanish Crown ruled, the language also became known as Spanish.