Juan de Ayolas (died c. 1537) was a conquistador born in Briviesca who explored the watershed of the Río de la Plata for the Spanish Crown. He accompanied Pedro de Mendoza on his 1534 expedition to colonize the region between the Río de la Plata and the Strait of Magellan and briefly succeeded him as the second governor of the region after Mendoza returned home in 1537.
Seeking supplies, he sailed up the Paraná River and founded a fort called Corpus Christi, as Sebastian Cabot had before him. Leaving Domingo Martínez de Irala at Puerto la Candelaria (modern Fuerte Olimpo), he sailed up the Paraguay River seeking a connection to Peru. He fought with the Guaraní, crossed the Chaco to the Andes, and seized some loot there but, when he returned, was killed with every man of his company by the Payagua.
Pedro de Mendoza
| Governor of New Andalusia
Domingo Martínez de Irala