Sebastián de Soto was a native of Guadalajara (Guadalajara province) and the son of Sebastián de Soto and María Barbáz. He came to New Spain with Viceroy Mendoza in 1535 and appears to have been connected to the Viceroy prior to his coming with Mendoza. Sebastián was present at the 1540 muster as an unassigned horseman. After the muster there is no further mention of him, so perhaps he died on the Expedition.
AGI, Pasajeros L.2, E.1258 [June 26, 1535, Sebastián son of Sebastián de Soto and María Barbáz, citizens of Guadalajara, with the viceroy] [certainly seems like him if he was with Mendoza];
AGI, Justicia, 337B [1537, witness (where?), more than 22 years old (b.<1515), answers questions on the characters of various persons, signed (no signature on copy), fol. 852r-853r];
AGI, Justicia, 258, pieza 1, “Relación de los salarios” fol. 798v: Nov. 1539, a sebastian de soto...Lx pesos]
1540, Feb.: Muster in Flint & Flint, Documents, Document 12 [two horses, elk hide jacket, head armor, native arms]