Christopher Columbus was born in 1451, in Genoa, Italy. His father was a land owning merchant. His mother's family was a well-established Genoa family. Columbus headed out to sea at a young age. His career at sea most likely began as a cabin boy or seaman.
In 1476, Columbus arrived in Portugal. There are some accounts that claim Columbus reached Portugal only after the ship he was sailing off the coast was sunk in a hostile fight and that Columbus was forced to swim ashore. In Portugal, he continued his involvement in maritime affairs. In 1478 or 1479 Columbus married Felip Moniz, from a well-connected Portuguese family.
Columbus was obsessed with travel to China all his adult life. He had read about Marco Polo's Journey and believed that there was a way to reach China by sailing to the West. Columbus did not have to convince people that the world was not flat. At the time, it was accepted by most educated people that the world was round. Columbus, however, insisted that the world was smaller than what was mostly accepted. He claimed that the total circumference (how large the world was at the equator) was 19,000 miles. (It is in fact 24,000 miles.)
Portugal at the time was the center of exploration. Columbus petitioned the King of Portugal to underwrite his quest for a westward passage to China. The King refused and in 1485 Columbus left Portugal for Spain.