The "Immortals" of Ancient Persia

Nice, succinct treatments of ancient Persia's elite corps of warriors called the Immortals can be found here and here.  Apparently, by the time Alexander the Great's time, there was another special force in Persia called the "Apple Bearers."  The name is not nearly as intimidating, but whether or not it had anything to do with Persia's defeat at the hands of Alexander, I can't say.