AGUIRRE, LOPE DE (1508-1561), Spanish adventurer. In 1559 he joined Pedro de Ursua's expedition to the Upper Ama zon, in search of El Dorado, and took part in the murder of Ursua and his lieutenant in 1561, after which Guzman was elected cap tain by the crew, with Aguirre as his master of the camp. The murderers declared themselves rebels, and sailed down the Ama zon, plundering and putting to the sword whole villages of Indians. Aguirre established a reign of terror on board ship, which culminated in the murder of Guzman, and his own self appointment to the position of captain. In July of 1561 the party Margarita Island, where they murdered the governor, robbed the royal treasury and proceeded to make incursions into the mainland of Venezuela. About this time Aguirre wrote and despatched an amazing letter to the king of Spain, accusing him of ingratitude toward himself, Aguirre, and his followers, and giving a full account of his own villainous exploits on the voyage.
Soon after, his men began to desert him and just when an attack was expected from Spanish troops, he was shot by his own fellow rebels, in Oct. 1561.
See R. Southey, Expedition of Orsua, and the Crimes of Aguirre (1821) ; and P. Simon, The Expedition of Pedro de Ursua and Lope de Aguirre in search of El Dorado and Omagua (1861) .