Diaz is a very common name in Spain (and in Portugal, where it is spelled Dias). As a matter of fact, it is the 14th most common surname in Spain, and Diaz ranks higher in a few Latin American countries, such as Argentina (#6), Chile (#4) and Peru (#8).
It is so widespread in Spain that it is nearly impossible to know where it originated, and even what it means. The most believed theories are that "Diaz" comes from the word "día," or "day," or that it comes from the first name Diego, as in "son of Diego." There are many branches of the Diaz family in Spain that you will also find more than one coat-of-arms, besides the one above.
The beginnings of the Diaz family on Guam present a mystery. In the 1727 Census, there is a single man named Antonio Diaz listed among the Spanish soldiers. He disappears in the 1758 Census and no Diaz is placed in the Spanish list. In the 1727 Census, there is a Filipino (Pampanga) soldier named Tomas Diaz, but he is still single. Did he eventually marry? Did he marry a Chamorro?
In the 1758 Census, in the Pampanga list, there are two boys, Jose and Juan Diaz, who seem to be the sons of Marta del Castillo, then married to an Arriola. Jose and Juan could have been her sons from her first marriage, to a Diaz; possibly the Pampanga soldier Tomas Diaz from the 1727 Census, but we can't be sure. For all we know, these two boys could be the sons of Antonio Diaz, listed in the 1727 Spanish list, or they could be the sons of someone else we don't know about.
Antonio Diaz (SPANISH)
Tomas Diaz (FILIPINO)
( 0 )
Juan Diaz (FILIPINO)
but who was their father?
Antonio Diaz (Spaniard)?
Tomas Diaz (Filipino)?
or another Diaz (unknown)?
By the 1897 Census, the Diaz family was centered on Hagatña and Sumay, and some had moved to Saipan. The Gayego clan is a well-known branch of the Diaz family in the Marianas. Nicolas Cruz Diaz had served as Alcalde (Mayor) of Tinian in the late 1800s. Tinian at the time had no permanent settlement of Chamorros; it was a place for raising cattle and other animals and produce to export to Guam and Saipan. Carolinians, and a few Chamorros, worked there but then left for either Guam or Saipan.
Recently, yet another Diaz line has started on Guam, with the Filipino but long-time Guam resident Judge Ramon Diaz, some of whose descendants have married into Chamorro families.