Latin American dictators are a gruesomely colorful bunch, but few caudillos can match Maximiliano Hernández Martínez, a general nicknamed "the Nazi warlock" who ruled El Salvador from 1931 to 1944. A fascist sympathizer who dabbled in theosophy, he massacred tens of thousands of his countrymen in 1932 to put down a peasant revolt. In 1944, he survived a coup attempt and launched savage reprisals but was forced from power weeks later by a general strike.

In his novel "Tyrant...