Complex sentence: While the other three men all returned to Spain, Estevanico was sold to Antonio de Mendoza, the Viceroy of New Spain, who was to use Estevanico as a guide in expeditions to the North.
Split into simpler sentences: While the other three men returned to Spain, Estevanico was sold to Antonio de Mendoza, the Viceroy of New Spain. He employed Estevanico as a guide in expeditions to the North.