In a Nutshell
Columbus was the first European to attempt to sail to China by sailing West across the Atlantic but he never actually landed on the mainland of North America. Since the Americas were already populated when he arrived at least one group of people had beaten him there. Archeological evidence shows that several Viking expeditions reached North America and there are fringe theories of other Pre-Columbus visits to America.
The Whole Bushel
Columbus’s trip to America is often claimed as a voyage of discovery. In many senses it was, but it was not the first trip to the Americas nor even the first European expedition.
Humans first crossed to the Americas from Asia during the last Ice Age. About 30,000 years ago a land bridge existed between Siberia and Alaska. These people can certainly be said to have discovered America quite some time before Columbus. But if you wish to overlook them, and they so often are, there were other discoverers of America.
The Icelandic Sagas talk of expeditions to the West which reached two landing sites- one called Greenland and one called Vinland. Greenland can be easily identified as the country we now call… er… Greenland. But it was thought that visits to Vinland we mythical.
In 1960 at a place called L’Anse aux Meadows in Newfoundland the remains of a Viking settlement were discovered. Settled around 1000AD the village included houses and a forge built along traditional Viking lines. The discovery shows that Columbus was at least 500 years too late to be called the discoverer of America.