Short answers, pulled from the story.
Spanish has about 519 million native speakers and roughly 636 million speakers in total when second-language speakers are included. It is the world's second-most spoken native language after Mandarin Chinese and the most widely spoken Romance language.
Spanish originated in the Kingdom of Castile in north-central Spain, evolving from the Vulgar Latin brought to the Iberian Peninsula by the Romans starting in 210 BC during the Second Punic War. According to Ramón Menéndez Pidal, it developed from local Vulgar Latin in an area centered on Burgos, then spread to Toledo, where the written standard was first developed in the 13th century.
Spanish is called castellano because the language came from the Kingdom of Castile, a name usually traced to castillo, meaning castle. The Spanish Constitution of 1978 uses castellano for the official language of the state, and the Royal Spanish Academy treats español and castellano as synonymous and equally valid.
Mexico has the largest population of native Spanish speakers and is the most populous Spanish-speaking country. Spanish is the official language of 20 countries in total.
About 75% of modern Spanish vocabulary is Latin in origin, including Latin borrowings from Ancient Greek. Roughly 8% of the lexicon, some 4,000 words, derives from Arabic absorbed during the Al-Andalus era in the Iberian Peninsula.
The Gramática de la lengua castellana, written by Elio Antonio de Nebrija in Salamanca in 1492, was the first grammar written for a modern European language. Its introduction was dated the 18th of August 1492.
Equatorial Guinea is the only Spanish-speaking country located entirely in Africa, where the Instituto Cervantes estimates 87.7% of the population is fluent. Spanish was also the official language of the Philippines from 1565 until 1973, and it is the official and most spoken language on Easter Island.