Gonzalo de Castilla was probably born in Córdoba (Córdoba) though the exact year is unknown. There are several individuals with the name Gonzalo de Castilla in New Spain, but we favor the man who accompanied doña Juana de Sosa in 1536. Not only did doña Juana marry don Luis de Castilla, a close ally of Viceroy Mendoza, but also she was the sister of the royal treasurer, Juan Alonso de Sosa, the brother-in-law of Vázquez de Coronado. It is also possible that Gonzalo was a relative of don Luis de Castilla in charge of Luis's future wife until she safely reached New Spain. If this logic holds, then his parents were Alonso González and Inés del Castillo. Gonzalo was present at the 1540 muster as a member of don Diego de Guevara's company.
Gonzalo del Castillo (there seems to be no de Castilla in the known documentary record)
Pre 1530:
?AGI, Pasajeros, L.1, E.1813 [to Indies in 1514, mother-Mari Álvarez, from Ávila]
?Millares Carlo y Montecón, Indice y extractos, I:301 [Dec. 5, 1525, locksmith, vecino of Mexico City]; I:#512 [April 26, 1527, locksmith]; I:563 [May 25, 1527, locksmith, estante in Mexico City, owes money]; I:575 [June 4, 1527, locksmith, estante in Mexico City]; I:611 & 612 [June 26, 1527, locksmith, poder from Hernando de Cáceres to him and Luis Hernández, platero, forming a company to exploit the mines in Michoacán] (Gonzalo de Castilla and a Luis Hernández are 1 name apart on muster); I:848 [Nov. 4, 1527, locksmith, estante in Mexico City]; I:943 [Jan. 7, 1528, locksmith, estante in Mexico City]; I:1161 [March 12, 1528, locksmith, estante in Mexico City, poder from Francisco Rodríguez]
?AGI, Pasajeros, L.1, E.3444 [Sept. 26, 1527, Gonzalo de Castillo, native of Azuaga, son of Lope Alonso and Marina Sánchez, vecinos of Azuaga (this one cannot be the locksmith who was in Mexico City by 1525)];
?Millares Carlo y Montecón, Indice y extractos, I:1300 [April 28, 1528, vecino of Mexico City]
1530-1540:
AGI, Contratación, 5536, L.4 [fol.42r-42v:May 5, 1536; Gonzalo del Castillo, son of Alonso González and Inés del Castillo, native of Córdoba, came to Nueva España in the company of doña Juana de Sosa (Juana married don Luis de Castilla)
1540-1550:
1540, Feb: Muster in Flint & Flint, Documents, Document 12 [3 horses, native arms, in the company of don Diego de Guevara, written as Gonzalo de Castillo]
1570-1580:
?Enciso Contreras, Testamentos [p.276: source: AGI, Contratación, 221, N.1, R.6, will of Alonso Díaz de la Pedrera, carta de pago from Gonzalo del Castillo, 3 pesos; will is 1578]