Johannes de Hartog was born on April 22, 1914, in Haarlem, Netherlands. He was a son of Arnold Hendrik, a Calvinist minister and professor of theology at Amsterdam University, and Lucretia de Hartog, a lecturer in medieval mysticism. De Hartog's vivid imagination was encouraged by his father. Johannes had an early love for the sea. At 10, he ran away to sea and became a cabin boy, called a ''sea mouse,'' on a fishing boat. His father had him brought back home, but when he was 12 he ran away to sea again, this time on a steamer in the Baltic. De Hartog later said his shipmates were ''as evil a collection of pirates as ever sailed the sea,'' but they took him under their wing and confirmed the boy's love of the sailor's life.