The medieval Spanish knight Rodrigo Díaz de Vivar was famously known by the nickname "El Cid." This name derives from the Arabic "as-Sayyid," meaning "the Lord" or "the Master," a title likely used by the Mozarabs or Arabs serving in his ranks. Apart from "El Cid," he was also known by the Spanish honorific "El Campeador," which translates as "the Champion" or "master of the battlefield," a title he probably earned during military campaigns under King Sancho II of Castile. Both names together, "Cid Campeador," are often used to refer to him in historical and literary sources.