Henry was born in 1394, one of the sons of the Portuguese King John I, founder of the Aviz dynasty. In 1415 he and his brothers lead the Portuguese army in the conquest of Ceuta, a Muslim stronghold in Morocco. There he first learned about the riches of the territory. From this moment on he started learning about the country, riches and trade of western Africa.
Prince Henry decided to try to give Portugal a share in these riches. Holding Ceuta did not work - it used to be one of the richest caravan cities, but that was lost when it became a christian city. The only way would be going around the Muslim territory, and go to the lands where gold, silver, and many more products came from for themselves.
It is sometimes thought that Henry was looking for a searoute to India, but, although he might have been, this certainly wasn't the main reason for his expeditions. Far more important was the wish to take part of the West-African trade. Another important goal was to find Prester John, a christian king that was rumoured to hold a large empire somewhere in Africa. If he would contact Prester John, perhaps together they could gain a decisive victory over the muslims. Prince Henry was a Crusader at least as much as a discoverer.
Henry established himself in Sagres, on the southwestern tip of Europe, far away from the court in Lisbon. There he brought together several important cartographers and instrument-makers. New, more precise maps were created, sailors got lessons in navigatory techniques, and a new type of ship was developed, the caravel, that combined cargo capability, maneuverability and seaworthiness, and thus was the ideal ship for exploring. Lagos, near Sagres, became a center for shipbuilding. The Age of Discovery was ready to get started.
He started sending out ships southward along the African westcoast. However, none of his men dared to go beyond Cape Bojador, a tiny cape somewhat south of the Canaries. They were afraid that beyond Cape Bojador the sea was so undeep that even one league (almost 5 kilometres) out of the coast, the sea was only 1 fathom (2 metres deep), that the currents were so strong that no ship would ever return and that no life would be found on the land. From 1424 to 1434 Henry sent out 15 expeditions, all of which did not dare to pass the Cape.
Then, in 1433, a squire called Gil Eannes, made an attempt. He too was too afraid, however, and returned empty-handed. Finally Henry's patience was at an end, and he made Eannes promise to go south again, and this time not to return without having passed the infamous cape. This time Eannes succeeded into doing what so many before him failed to do. To avoid the shallows near the Cape, he sailed westward into the open sea, and when he turned east again, he found himself on the south side of the Cape. He found the country desolate, but not deprived of all living. Finally the barrier of fear had been broken. Eannes deserves his name to be among those of the most important explorers of our world.
From this time on Henry's men reached further south, every year (well, not really, sometimes one or more years were missed when troubles within the Portuguese royalty or fights with the Muslims took too much of prince Henry's time) going a bit further south:
It was around this time that Henry's voyages began to bear fruit. Slaves and seals, and later other trade articles as well, began to be sailed from the African Coast to Portugal. An important view on the Portuguese trading voyages can be got from Alvise da Cadamosto, a Venetian trader who took part in the voyages to contemporary Senegal, and wrote a book on his voyages. He is also credited with the discovery of the Cape Verde Islands.
By the time Prince Henry died, in 1460, the Portuguese had reached Cape Palmas (Liberia), and a trading post had been established in Arguim (an island near Cape Verde).
Daniel J. Boorstin: The Discoverers. Harry N. Abrams, New York, 1983/1991.