The war began when William Walker, an American filibuster, or person engaged in unauthorized warfare against a foreign country, overthrew the government of Nicaragua in 1856 and attempted to conquer the other nations in Central America, including Costa Rica, in order to form a private slaveholding empire. Costa Rican President Juan Rafael Mora Porras called upon the general population to take up arms and march north to Nicaragua to fight against the foreign invader. This started the Filibuster War. Santamaría, a poor laborer and the illegitimate son of a single mother joined the army as a drummer boy. The troops nicknamed him "el erizo" ("the hedgehog") on account of his spiked hair.