Perhaps he was hated and he might have deserved it, but that doesn't change the fact that he sailed to the Americas, leading to the knowledge of such a continent. Colombus changed the world, even a hated jerk as he might have been.

He actually sailed that direction in hopes of finding Asia (they knew the world was round for quite a while by then), which is why he mistook the people living there as Indians, thinking he landed in the "Indies." It was found out where he really landed (it was the Caribbean), but the name forever stuck.