Alonso Castillo Maldonado, early Spanish explorer and Indian captive, a native of the Spanish university town of Salamanca, was the son of a physician and Aldonza Maldonado; both his parents were members of the Spanish nobility. As a well-bred but impoverished hidalgo, Castillo sought fame and fortune in the New World. He volunteered in 1527 as a captain in the expedition of Pánfilo de Narváez to Florida. After the expedition abandoned its attempt to go from the area of present-day Tampa, Florida, to Tampico, Mexico, by land, Castillo and Andrés Dorantes de Carranza were placed in joint command of a boat. In early November the makeshift vessel bearing Castillo and some forty men, including Cabeza de Vaca, was wrecked on or near the western extremity of Galveston Island. In the spring of 1529 a party of twelve, led by Dorantes and Castillo, started south along the coast; the survivors eventually arrived in Matagorda Bay. Castillo is credited with introducing faith healing among the coastal Indians. His ritual consisted of prayers and a gentle blowing of breath on the bodies of afflicted natives. Dorantes and Cabeza de Vaca were among his pupils, and Castillo's quiet demeanor and piety are credited with transforming Cabeza de Vaca's mechanical religiosity to genuine devoutness.
After nearly seven years of precarious existence among hostile Indians, Castillo, Dorantes, Estevanico, and Cabeza de Vaca escaped inland. They were the first Europeans to traverse Texas. Traveling a circuitous and now disputed west-by-northwest route, they may have passed near the sites of San Antonio, New Braunfels, Austin, Big Spring, and Pecos. After a brief trek through the south part of what became New Mexico, they reentered and left Texas at El Paso in late 1535. Walking southward through Sonora and Sinaloa, Castillo and his companions were reunited with their Spanish countrymen north of Culiacán in 1536. From there they traveled to Mexico City for an audience with Viceroy Antonio de Mendoza.
Castillo chose to continue his career in the New World. After a brief visit in Spain he served as a treasury official in Guatemala (1545), and as an encomendero he later enjoyed one-fourth of the revenues of Tehuacán in New Spain. Castillo appeared as a witness in a lawsuit in 1547, and he is believed to have died in the late 1540s.