Diego.

From an Iberian name, Latin Didacus, recorded from the 8th century, of unknown origin. Various suggestions include Greek, Basque and Celtiberian derivation, without wide acceptance of any proposal. The name Didacus is recorded in the vernacular as Diaco, Diago by the 10th century. The earliest record of the form Diego is of the late 11th century. Diego is the standard form in Spanish by the 14th century. There has been a widespread folk etymology, current from at least the early 19th century, to the effect that the name is a reanalysis of Latin Sanctus Iacobus (“Saint James”), i.e. Sant-Yago read as San-Tiago, whence Diego. It has been common practice in Spanish to equate Jacob, Iacobus with Diego throughout the 19th and 20th centuries, e.g. the Enciclopedia Espasa-Calpe (1920) lists a number of Italian and German saints named Jacobo, Jakob under Diego. This derivation has been recognized as folk etymological since at least the 1970s.