Rodrigo (or Ruy) Díaz de Vivar (Vivar (Burgos) c. 1044–Valencia, 10 July 1099), known as El Cid Campeador, was a Castilian nobleman, then military and political leader who 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 Alfonso VI, fighting against the Moors in the early Reconquista. Later exiled by the king, El Cid left service in Castile and worked as a mercenary for other rulers, both Muslim and Christian.
"El Cid" is derived from the word al-sīd in the Andalusian Arabic dialect (from the Arabic sayyid, "chief" or "lord," a title of respect), while the title El Campeador (the champion) was granted by his Christian admirers and derives from the Latin campi doctor. These titles reflected the great esteem El Cid had among both Moors and Christians, as well as his fighting ability; Henry Edwards Watts wrote that el campeadorcampeador was a man who had fought and beaten the select fighting-man of the opposite side in the presence of the two armies."
"El Cid" was pronounced /el tsið/ (IPA) in mediaeval Spanish, but /el sið/ or /el θið/ in modern Spanish (depending on dialect).