Prince Henry the Navigator was a Portuguese explorer, soldier and prince. Although Prince Henry rarely participated in explorations, he sent many expeditions from Portugal to the west coast of Africa, and was responsible for Portugal's influence in the Great Age of Exploration. Because of Prince Henry, Portuguese explorers were the first to sail to Africa's Gambia River.

Prince Henry's sponsored explorations that accomplished much for Portugal. Not only did his expeditions succeed in mapping much of the coast of west-Africa, but they also succeeded in spreading Christianity, defeating Muslims (enemies of the Portuguese at the time), and establishing new trade routes. Prince Henry's primary motivation, however, for exploring the west coast of Africa was to see how far Muslim lands extended to the south (to defeat them), and to find the legendary Christian empire of the priest-king Prester-John (who didn't actually exist). In 1419, Prince Henry started the first school of navigation at Sagres, Portugal. The goal of the school was to train people in navigation, map-making and science to prepare them to sail around the west coast of Africa.

Prince Henry's school of navigation resulted in a breakthrough for Portuguese navigation. Before Prince Henry, sailors and navigators refused to sail toward Africa. They were scared of sea monsters and boiling water near the equator. In fact, no sailor had ever sailed into the "Sea of Darkness", which the Portuguese considered to be any part of the ocean south of 27 degrees north latitude (about Cape Bojador). Prince Henry's school sent 14 expeditions into "The Sea of Darkness". Prince Henry himself even convinced some explorers to go further south. Prince Henry's influence was the first step in finding the vaunted sea route to the Indies.