The name in portuguese is "Infante Dom Henrique", he was a Prince but not a king, of Portugal.
From 1415 onwards he was the mastermind behind a massive plan of exploration, which would last centuries, charting and discovery of unknown seas and lands for Portugal.
He created a "school of navigation" where he summoned the best minds in Europe in terms of geography, astronomy, mathematics and sailing.
By himself he sailed very rarely, only in 1415 together with his father the king when invading the most important sea port of the moors, Ceuta, with a massive armada of close to 200 ships (it would remaine for centuries the largest armada) and on a few other occasions, never far from Portugal.
However, because of his plan, Portugal was the absolute pioneer in the Age of Discoveries, just as an example, even Columbus lived and studied in Portugal before going to Spain and by 1492, when he reached America, the portuguese had already explored the entire african west coast and discovered the Sea Route to India, sailing around Africa, in 1488, 4 years before Columbus tried to do the same thing sailing west.
The portuguese were the first europeans ever to sail around Africa, discover Brazil, sail and chart the entire India Ocean, all its islands and all countries surrounding it, reach China by sea, probably discovering Australia, reach Borneo and New Guinea and the first europeans to reach Japan in 1543.