The legend of El Dorado was about a fabulously wealthy city of gold and the king who ruled over it. The story sprang up shortly after the first Spanish explorers landed in Central and South America.

Local people told tales of a rich king who plastered his body with gold dust and then dived into a sacred lake to wash it off. Afterward, he would toss gold into the lake as an offering to the gods. The Spanish called the king El Dorado—The Gilded One—because his body was gilded, or covered, in gold. As the tale spread, the city he ruled came to be called El Dorado. Eventually, the meaning of the name changed to include any mythical region that contained great riches.

An early version of the El Dorado legend placed the city near Lake Guatavita not too far from modern Bogotá, Colombia. The story was based on the Muisca people who performed a ceremony similar to that in the legend. The Muisca king, covered with gold dust,...