The bear, which won the sympathy of millions because of his controversial upbringing, became a global celebrity, doubling ticket sales at Berlin Zoo. His official logo has raised over $14 million for the zoo and has been used on a wide range of merchandise, including cuddly toys, books, CDs, credit cards and souvenirs.
The German Mint issued 25,000 silver commemorative Knut coins. The superstar bear became a symbol of Germany's campaign against global warming and even Chancellor Angela Merkel recently admitted she liked the bear.
A crowd of admirers from all over the world applauded and sang happy birthday, when Knut was given a large birthday cake made of boiled rice, bananas and raisins and decorated with a wooden candle. Zoo visitors were offered a piece of a huge oval-shaped birthday cake, made from 300 eggs and 30 lbs of flour and sugar.
"My birthday wish for Knut is that he is happily transferred to another zoo - in a big compound with a female partner," his keeper, Thomas Dorflein, said.
Knut and his twin brother were abandoned by their mother, Tosca, a 20-year-old traumatized circus bear, shortly after their birth in December 2006. Zoo keepers used a fishing net to remove the cubs from their mother's compound, but Knut's brother died in an incubator on the fourth day.
Zoo keeper Thomas Dorflein came to Knut's rescue. He became his surrogate mother, hand-feeding the cub every half hour, rubbing his body with baby oil, and singing Elvis Presley songs to help him sleep.
After the bear had gained more than 240 pounds in weight, Knut's keeper was ordered to keep his distance, as the animal was potentially dangerous.
"Knut is not like my child and he does not arouse the same kind of emotions," he said. "For me Knut is always an animal."
The Berlin Zoo faced criticism from animal rights activists who claimed it was unacceptable to raise a wild animal by hand, some even called for the zoo to put him to sleep.
