Where the Diaz name comes from

Diaz is a patronymic of Diego, and the cleanest proof is El Cid: his real name was Rodrigo Diaz de Vivar and his father was called Diego. The name was first found in the Kingdom of Castile and dates from the Visigoth period. Dias is its Portuguese cognate, and some American Diaz families came by way of that spelling rather than the Spanish one. As of 2014 more bearers of the name lived in Mexico than anywhere else, a little over a fifth of them.