John Thomond O'Brien

By most sources John Thomond O'Brien was born in 1786 in Baltinglass, Co. Wicklow, the son of Martin O'Brien and Honoria O'Connor. Edmundo Murray's dictionary entry has him reaching Buenos Aires in 1812 to open a merchant house before joining the army; Tim Fanning's 2020 biography says he emigrated in the 1810s to profit from the textile trade and enlisted as a cavalry officer in 1813. He fought in Uruguay under General Soler, joined San Martín's Mounted Grenadiers in 1816 and, after Chacabuco, was made captain and aide-de-camp to San Martín. He fought at Cancha Rayada and Maipú and in the Peru campaign, became a colonel in 1821 and, in Peru, a general in 1835. Fanning adds that he launched a ship on Lake Titicaca and organised Irish support in Buenos Aires for O'Connell's Catholic Emancipation campaign.

In 1826 Buenos Aires figures commissioned him to recruit Irish immigrants. After two years in Ireland he had little success, but he met John Mooney, whose emigration Murray describes as the start of the Irish chain from the Westmeath, Longford and Offaly area. McKenna says O'Brien insisted that emigrants have their own chaplain and physician, and that he was to recruit only "moral and industrious" people.

He fell out with Rosas and was imprisoned in the 1830s. Murray says he was released after pleas from Rosas's daughter and British diplomatic pressure; the Mendoza government says he had been serving Santa Cruz's Peru–Bolivian Confederation, then at war with the Argentine Confederation. In the 1840s he represented the Montevideo government in London and Paris, published a London pamphlet on the River Plate war and navigation in 1845 and was Uruguay's special envoy to the United Kingdom in 1848. The Mendoza government also records accounts that he was a British agent sent to watch San Martín and Alvear.

He died in Lisbon on 1 June 1861 on his way back to South America. His remains were brought to Argentina in 1938 with an official funeral, and a town in Bragado bears his name. In January 2017, for the bicentenary of the Crossing of the Andes, they were moved from Recoleta to the Campo Histórico El Plumerillo in Mendoza.