Knut the polar bear

Visitors watch polar bear cub Knut in the Berlin zoo, March 24, 2007. Knut, the polar bear who became a global celebrity as a cute cub, died in at the Berlin zoo March 19, 2011 at the age of four. Knut, the first polar bear born at the zoo for more than 30 years, was rejected by his mother and fed instead by his keeper Thomas Doerflein. Thousands of visitors came to watch keeper and cub playing together, and Knut's fame soon spread around the world. The cause of death was unknown and he will undergo an autopsy.

Knut has his first public appearance with his keeper Thomas Doerflein in the Berlin zoo, March 23, 2007.

Knut playing with a blanket at his enclosure of the Berlin zoo, March 28, 2007.

Knut plays with a foot of his minder Thomas Doerflein at the zoo in Berlin, June 11, 2007.

Knut eats his one-year birthday "cake" at the Berlin zoo Dec. 5, 2007, in Berlin, Germany. Zoo officials celebrated Knut's one year birthday by inviting the public and the media to watch Knut eat his cake, whose ingredients included rice, potatoes, carrots and a whole fish.

Knut is refelcted in a window as he takes a bath Jan. 11, 2008 in his enclosure at the zoo in Berlin.

Knut takes a bath in his outdoor enclosure at the zoo in Berlin, Germany, Aug. 6, 2009.

Knut swims in common duckweed at the zoo of Berlin, Sept. 14, 2009.

Knut, right, and Giovanna, a female polar bear on loan from the Munich zoo, play tug of war as they swim in their enclosure at Berlin's Zoologischer Garten zoo Jan. 8.

Polar bears Knut, left, and Giovanna cuddle at their enclosure at the Berlin zoo on March 4, 2010 in Berlin, Germany.

Knut interacts with with six-year-old visitor Nane and her cushy polar bear "Knut" at the Tiergarten zoo in Berlin on Oct. 19. German newspapers reported today that the world famous polar bear is being bullied by his fellow polar bears in their enclosure in the Berlin zoological garden.

Knut rolls in the snow in his enclosure at Berlin's Zoologischer Garten zoo, Jan. 8, 2010.

Knut stands in his enclosure, March 26, 2010.

Knut yawns in his enclosure at the zoo in Berlin, Dec. 10, 2010.

Children stand in front of polar bear Knut's enclosure at the Berlin zoo on March 21, 2011. Germany was in stunned mourning after the sudden and premature death of Knut, Berlin's world-famous polar bear, who died on March 19. Zoo visitors signed a condolence book, left notes, flowers and candles in tribute to the beloved bear.