Erikson (c. 970 – c. 1020), a famed Norse explorer, founded a settlement in Vinland, now part of Canada.
UPDATED: Link to President Obama's 2010 proclamation: http://www.whitehouse.gov/the-press-office/2010/10/08/presidential-proclamation-leif-erikson-day
Here's a link to President Obama's 2009 proclamation for that year's Leif Erikson day: http://www.whitehouse.gov/the_press_office/Presidential-Proclamation-Leif-Erikson-Day/
In addition to the federal observance, some states officially commemorate Leif Erikson Day, particularly in the Upper Midwest, where large numbers of people from the Nordic countries settled. In 1930, Wisconsin became the first state to officially adopt this holiday, thanks to efforts by the Norwegian-American initiator, Rasmus B. Anderson. A year later Minnesota followed suit. In 1963, the U.S. Representative from Duluth, John Blatnik, introduced a bill to observe it nationwide. The following year Congress adopted this unanimously.
October 9 is not associated with any particular event in Leif Erikson's life. The date was chosen because the ship Restauration coming from Stavanger, Norway, arrived in New York Harbor on October 9, 1825 at the start of the first organized immigration from Norway to the United States.