The Leif Erikson one is very subjective though; you could celebrate:

• The first humans to cross the Bering Strait, which is a long extinct lineage
• The earliest ancestors to settle the Americas, whom we don't even know the descendants of
• The first Europeans to reach the Americas, ie Leif Erikson (Polynesia did it much later)
• The first people to cross an ocean to get to the Americas, most likely Polynesians but possibly Columbus
• The first Europeans to form a permanent settlement in the Americas, ie Columbus
• The founders of the forerunner to the US, ie Walter Raleigh & co
• The founding fathers for founding the US

And plenty more I'm sure you could come up with