Knut has also had to contend with competition. With all the fanfare of a movie premiere or record release, Nuremberg city and zoo officials introduced their own cub, Flocke in April.
A week later, Stuttgart's Wilhelma zoo presented little Wilbaer, another adorable white ball of fluff.
But that has barely affected Knut's status as the Berlin Zoo's main attraction. The zoo has credited Knut with a 27 percent increase in visitors in 2007 and profits of nearly euro6.8 million ($8.6 million) from the products that bore Knut's image, including stuffed animals, T-shirts, mugs and DVDs.
Nevertheless the zoo insists it must do what is best for the young polar bear - finding him a suitable home and mate - even if it means bidding goodbye to the former Vanity Fair "coverbear."
"The survival of the species is more important than any individual," bear keeper Heiner Kloes told The Associated Press on Thursday.
Knut currently lives in a small section of Berlin's polar bear enclosure, home to four other polar bears, including Knut's parents Tosca and Lars. That means there is no extra space for Knut.
Kloes said he wouldn't consider keeping the young bear - who will celebrate his second birthday with a cake of fruit and without the big party of last year - instead of his father, because by the time Knut is sexually mature the two other females will be too old to bear cubs.
Polar bears reach sexual maturity around age 6.
"I won't hang on to Knut if it means keeping him with an old lady," Kloes said.
Doris Webb, 65, has followed Knut since he was first presented to the world by the keeper who raised him by hand after he was rejected by his mother. Since April she has gathered more than 21,000 signatures in support of keeping him in Berlin.
"We want to show how important it is for Berlin, for the people here - and for Knut himself," she said.
Under a deal with the Neumuenster zoo, which owns Lars, it has the right to Knut. Zoo manager Peter Druewa told The Associated Press Thursday that Knut would have to move if the Berlin Zoo is not ready to invest in a new enclosure for him.
"If Berlin doesn't want to build a new enclosure - or expand one of the existing ones - we'll need to find a new place for him," he said.
But Knut clearly retains some traces of his former glamor and there is no shortage of potential suitors who would be happy to offer a suitably roomy new home for him and a future mate.
Web site Unibet is even running odds on the zoo likeliest to get the bear, with Zoom Erlebniswelt in Germany the top contender, followed by Tierpark Neumuenster in Germany and Sweden's Orsa Bjornpark. Also tipped but at longer odds are zoos in Norway, Finland, Denmark, Estonia and the decidedly unpolar Spain.
Torbjorn Wallin, chief executive of Orsa Gronklitt AB which runs the Orsa bear park 200 miles (320 kilometers) northwest of Stockholm, said his company has been in talks with Berlin Zoo about Knut's future for the past 18 months.
Wallin declined to discuss financial details, but said a suitable mate, rather than money had been the main focus in discussions with Berlin.
Although Orsa - which is going to be Willbear's future home - is a hot contender in the race to take over Knut, Wallin said others had shown interest too.
"Of course there are others - it's the world's most famous animal," he said. "It's as if Madonna would move to Stockholm."
