Who is the tennis player known as 'King of Clay'?

Rafael Nadal

Which spice commonly flavors sweet potato dishes served at Thanksgiving? In Risk, how many cards must you turn in the first time you trade cards for armies? In culinary terms, what phenomena causes browning and flavor changes when food is cooked at high temperatures? What gas was historically used in airships before helium became common? What Native American is credited with aiding the Pilgrims during their first winter in America?