Sad news from Germany: Knut, the world's most famous polar bear, is dead. The 4-year-old bear was found in his enclosure this morning, though the cause of death isn't known. Knut became an international sensation after being abandoned by his mother at the Berlin Zoo, then raised by human keepers. He drew millions of visitors, notes Bloomberg. To catch up on all things Knut, click here. (More Knut stories.)