Nickname of Rodrigo (or Ruy) Díaz de Vivar (born circa 1040, Vivar, near Burgos– 10 July 1099, Valencia), also called El Cid Campeador, was a Castilian nobleman, military leader, and diplomat. After being exiled, he conquered and governed the city of Valencia. Rodrigo Díaz was educated in the royal court of Castile and became the alférez, or chief general, of King Alfonso VI of Castile, and Alfonso's most valuable asset in the fight against the Moors. El Cid became the subject of a Spanish national epic.
References
Wikipedia
Spanish epic poem Cantar de Mio Cid.
Etymology
From el, the, + Cid, from the dialectal Arab word سيد(sïdi or sayyid, “lord, master”); thus "El Cid" means "The Lord". The title "Campeador" is a word from Vulgar Latin that can be translated as "champion" or "master of military arts".