Spanish-American explorer, soldier, and lieutenant governor (1591–93) and governor (1602–09, 1614–18) of the Spanish district of Río de la Plata in South America.

Hernandarias was known for his protection of the Indian population, for establishment of closer ties between the church and the civil authorities, and for encouraging the establishment of Jesuit and Franciscan missions. An efficient and incorruptible official, he inadvertently caused economic setbacks to the area by rigidly enforcing the laws against smuggling, an activity that had become virtually institutionalized under more lenient governors. Hernandarias founded the city of Corrientes (now in Argentina) and helped develop Buenos Aires, Santa Fe, and Asunción. During his second term as governor, the Río de la Plata was divided into two administrative units, one in Buenos Aires and another in Asunción, each with its own governor.