The Gaucho stands as one of the best-known cultural symbols of Argentina.     This rough, tough, free-riding horseman of the pampas, a proud cousin of the North American cowboy is maintained in Argentine culture as the perfect Argentinean embodiment, the very essence of the national character.   He usually spent most of his time on horseback roaming the ranchlands and has been elevated to the level of myth, celebrated in both song and prose, and well endowed with the virtues of strength, bravery and honor.