There didn't seem much to Knut the polar bear when the one-year-old cub went on public display for the first time at Berlin Zoo in March 2007. A ball of white fluff, a youthful inquisitiveness and those black, innocent eyes staring out at the strange, unnatural world of his captivity.
Almost four years to the day later, Knut was lying face down dead in the pool of his compound having collapsed suddenly with suspected heart failure. Rejected by his mother at birth and raised by his keeper, Knut's life incorporated a multi-million-euro industry in Knut paraphernalia, a court battle over his ownership, calls for his death, and then for his castration, and an ongoing debate about the ethics of keeping big wild animals in confinement.
Knut died on Saturday afternoon at the age of four. In the wild he could have expected to live to 15 or 20, while captive polar bears are known to be capable of living twice that long, being freed from the constraints of hunger and the bitter Arctic climate. Almost as soon as Knut was born, his existence prompted controversy. Was it right to hand-rear such an animal or should nature be allowed to take its course, which in this instance would have almost certainly meant witnessing the spectacle of ursine cannibalism? His mother, Tosca, was a former circus animal from East Germany and was herself probably traumatised by her treatment in early captivity. She rejected both Knut and his twin brother and, left to her own devices, would have probably killed and eaten both cubs.
Knut and his twin, then the size of a guinea pigs, were hauled out of the polar bear's compound by keepers using a fishing net. His brother died a few days later, but Knut survived with the help of his keeper, Thomas Dörflein, who bottle-fed him around the clock and even taught him to swim.
Knut flourished and was the first polar bear to be born and survive in the Berlin Zoo for more than 30 years. His survival was a tribute to Mr Dörflein's care. The keeper slept on a mattress by the cub's sleeping crate ready with a bottle of milk, and made sure the cub was kept healthy. Mr Dörflein, who died in 2008 of a heart attack at the age of 44, became a minor celebrity but his fame was nothing compared Knut's. The cub appeared with Leonardo DiCaprio on the cover of Vanity Fair, courtesy of the photographer Annie Leibovitz. The German National Mint produced 25,000 silver coins in his honour, and his image appear on postage stamps and countless items of memorabilia.
Knut's celebrity status was helped no doubt by his photogenic qualities but also by the public outcry that followed comments allegedly made by a German animal activist who had dared to suggest that Knut should have been put down rather than forced to live the degrading life of a domestic pet. Children stormed Berlin Zoo, holding up placards reading "Knut Must Live" and "We Love Knut". The zoo responded by promising that no harm would come to him and rejected the notion that it would be kinder to kill him rather than let him be raised by human hand.
Just to make sure that no one else was able to cash in on Knut's commercial potential, the zoo registered "Knut" as a trademark. It also fought a legal dispute for ownership of Knut with Neumünster Zoo, which owned Knut's father. The dispute was finally settled after Berlin Zoo agreed to pay €430,000 (£360,000), which allowed Knut to stay in the city of his birth.
Berlin Zoo is estimated to have made millions out of Knut. It sold some 2,400 stuffed Knut toys within weeks of his first public viewing. Yet, as Knut grew older, his obvious charms began to fade with his fur, which turned from brilliant white to dirty yellow.
The small ball of fluff the public fell in love with in 2007 ballooned out to nearly 300 pounds in weight, thanks partly to Knut's taste for croissants. But he also appeared to have developed an addiction to applause, going into a morose sulk when he wasn't surrounded by his adoring public.
According to Peter Arras, a German zoologist, Knut had developed psychopathic tendencies that would prevent him from engaging in social interaction with females. If Knut couldn't breed, so the argument went, what was the purpose of keeping him in captivity?
This goes to the heart of the debate about the purpose of zoos in the 21st century. Many conservationists argue that their prime aim should be as breeding centres, either to replenish captive stocks of animals or as places where endangered animals might be bred for later re-introduction to the wild.
Colin Tudge, author of Last Animals in the Zoo, said that captive breeding has had two notable successes in recent years. The California condor and the Arabian oryx would both have been extinct now in the wild had it not been for successful breeding programmes in captivity, Mr Tudge said.
"Some animals do well in captivity, but some do badly," he said. "Polar bears are among those that do not do well. Zoos tend to treat them like walruses, putting them on slabs of wet rock, when really they are bears and behave like bears when put in that sort of environment.
"Polar bears are going to need some serious conservation efforts soon, but you have to think in terms of a few hundred individuals for a captive breeding programme and you need the space in which to keep them – although they don't all need to be kept in once place," he added.
The long-term future of polar bears, threatened by the shrinking sea ice of the warming Arctic, was not helped by the short, captive life of Knut.