Juan Díaz de Solis
Although Europeans first arrived in, what is now South America, in 1502 with Amerigo Vespucci, Juan Diaz Solis was actually the first one to explore Argentina in 1516 (InfoPlease.com).
Juan Diaz de Solis

Solis was most likely born in Seville, Spain; however, others argue that he was actually born in Portugal (Wikipedia.com). His navigation career hit a high point when he led the navigation through the Yucatan and Brazil in 1506-1508 (Wikipedia.com). He was then promoted, after the death of Amerigo Vespucci in, 1512; Juan became Pilot-Major of Spain.

Tragically, while sailing up the Uruguay River, Solis and his eight companions were attacked by the local tribe of Charrua (Wikipedia.com). Only some crew members survived the attack. They came back to Spain and reported that Solis, and the other crew members were killed and then eaten. However, his death is quite the controversy. Some believe that Solis was killed in a mutiny and his crew lied about the attack of the Charrua (Wikipedia.com).