An Italian explorer who rediscovered a continent that most Europeans at the time had no previous knowledge of, and whose voyages set off further
exploration and
colonization of this "
New World," resulting in his being credited for its discovery.
Things CAN be discovered more than once. In general, people in Europe didn't know about the Americas before Columbus' voyages, and the resulting
colonization means that most of the people living in the Americas today are at least partially descended from
Europeans. No one alive today who says that Columbus discovered America actually thinks the land was uninhabited when he found it. The proper understanding is that, from a
eurocentric point of view, Christopher Columbus discovered America, which is true.