All of the reindeer who pull Santa's sleigh are male. The female reindeer, called does, are responsible for caring for the younger reindeer and maintaining the reindeer herd. The males, called bucks, are the ones who are trained to fly and pull the sleigh. The most famous buck, of course, is Santa's lead reindeer, Rudolph, who is known for his bright red nose and his ability to guide the sleigh through even the thickest fog and snowstorms.