A boy genius, Walker graduated from the University of Nashville at age 14 and received law and medical degrees from the University of Pennsylvania by age 19. However brilliant he was as a student, he failed as a doctor, lawyer and journalist. In 1849 he tried his luck, also unsuccessfully, in the California Gold Rush. His mind increasingly unbalanced, Walker came to believe that his true calling in life was to be a soldier of fortune. Not just a solider, but a leader of soldiers. To that end he joined a “liberation” expedition into Baja Mexico, sponsored by a pro-slavery group, the Knights of the Golden Circle. Before being driven out of Mexico, he egotistically declared himself, “President of Sonora and Baja California.”

After taking over Nicaragua’s government, Walker immediately legalized slavery. But his grandiose schemes ran afoul of Cornelius Vanderbilt, the powerful North American millionaire who owned large business interests there and hoped to build a trans-ocean canal through Lake Nicaragua. Vanderbilt encouraged Costa Rica to go to war and Walker conveniently supplied an excuse. With pro-slavery interests backing him (they hoped to expand the pool of potential slaves), Walker and a few thousand men (known as “filibusters”) invaded Costa Rica in March 1856. President Mora raised an army of 9,000 Ticos and marched on Walker’s encampment, headquartered in a large farmhouse in Guanacaste province.

On April 11, Juan Santamaría, a Costa Rican drummer boy, torched Walker’s farmhouse roof before dying in a hail of bullets. Santamaría became a national hero and the old farmhouse is now a national monument in the middle of Santa Rosa Park. The international airport in San José is named Juan Santamaría in his honor.

Tragically, after driving Walker out of Guanacaste and Nicaragua, returning soldiers brought back cholera and an ensuing epidemic killed 20% of Costa Rica’s civilian population. Walker later met his own fate in Honduras in a way that showed how demented he had become. In 1857 he tried to conquer Nicaragua again, but was taken prisoner. Paroled in 1860 he sailed to Honduras, seized a port customs house, and immediately declared himself “president.” Flushed out by Honduran soldiers, he took refuge on a British man-of-war but, after insisting he was the rightful President of Honduras, they put him back ashore. An army firing squad promptly executed him.