Knut, polar bear cub
In this March 23, 2007 file photo, Knut, the polar bear cub, has its first public appearance with his keeper in the Berlin zoo. A Berlin zoo official says world-famous polar bear Knut has died. Bear keeper Heiner Kloes said that four-year-old Knut died Saturday afternoon while alone in his compound. He says the cause is not yet clear. (AP Photo/Markus Schreiber)