The documentaries that showed him strumming Elvis's "(You're The) Devil in Disguise" on a guitar as he lulled the world's most famous polar bear to sleep were enough to win the hearts of millions of Germans.
This week, Thomas Dörflein, the Berlin zoo keeper who raised Knut from cub to full maturity, was found dead in mysterious circumstances in a friend's Berlin apartment. (Reports suggested the cause was cancer or a heart attack, but ruled out suicide.) It emerged that it wasn't only the bear who had been receiving bucketloads of fan mail. With his endearing manner, thick black beard and shoulder-length hair swept back in a ponytail, Dörflein, who was just 44, was an unlikely heart-throb who had been deluged with letters from admiring women. According to reports yesterday, in the past few weeks the keeper had been fending off groupies every time he left the apartment he shared with his girlfriend, Daniela.
Berlin was in mourning yesterday following the news of the keeper's death. "Everyone wanted to be like Thomas Dörflein," is how Berlin's BZ newspaper put it, "he not only cared for Knut; he nurtured our desire to see harmony between man and beast."
Klaus Wowereit, Berlin's mayor, said the city had lost an important symbol. Berlin Zoo itself described the keeper's death as tragic and a "great loss".
So what was it about this man that captured the German imagination? His appeal, of course, had everything to do with the other half of his double-act, the bear Knut. Their relationship became symbiotic not long after photographs and television footage of the tiny, snowy-white and initially blind bear were released, following the animal's birth at Berlin Zoo in December 2006. He had been rejected by his mother, a disturbed East German circus bear called Tosca, and under natural conditions Knut would have died shortly after birth.
Dörflein came to the rescue. For nearly 18 months, the keeper acted as a surrogate mother, hand-feeding his charge day and night with baby bottles full of milk, rubbing his body with baby oil, and playing him sentimental Elvis hits songs. He even christened the bear with an Old Norse name: "He just looks like a Knut," was how Dörflein justified his choice.
By late last year, however, Dörflein, who had practically given up life with his own family to look after Knut, appeared to have had enough. He said that he could wish the bear no better first-birthday present than permanent separation. There had been fears that Knut was becoming dependent on his human parent and the zoo banned physical contact between the two in July 2007. Dörflein defied the ban, however, and continued to enter Knut's enclosure at Berlin Zoo until February this year. But he had misgivings.
"Some day soon, Knut and I will have to split up," he said in an interview last year, adding that the bear needed a bigger compound. Berlin Zoo has been attempting to find a new home for Knut since then.
The extraordinary man-bear relationship became a media saga. Documentaries were pumped out by German television stations, and acres of print were devoted to the bear in the nation's popular press. When Knut first appeared in public at Berlin Zoo in March 2006, more than 500 journalists were present to record the event. Last year, the bear even appeared on the cover of the German edition of Vanity Fair (without Dörflein).
Conservative estimates put the profits that Knut has generated for Berlin Zoo at €10m. Hundreds of cuddly white Knut toy bears are sold as souvenirs to Berlin visitors daily, 25,000 silver commemorative Knut coins have been issued by the Federal Mint as collector's items and Berlin newspapers offer their readers Knut porcelain figurines at €148 apiece. A Hollywood film starring Knut opened in German cinemas this week.
But Knut's celebrity status prompted animal psychologists to warn earlier this year that the bear had developed psychopathic tendencies. Several suggested that Knut had become addicted to humans and their company and would never manage to live successfully with other polar bears or find a mate.
Berlin Zoo has been attempting to find Knut another home since the beginning of the year, albeit without success. At the same time, zoos across Germany have been involved in a protracted debate about the pros and cons of keeper-raising polar bears that have been rejected by their mothers. Some zoo directors argued that the practice was unnatural after another baby polar bear – also rejected by its mother – was born under similar circumstances at Nuremberg zoo this year.
For his part, Dörflein, who is survived by two grown-up children, aged 21 and 17, always denied suggestions that he had become emotionally involved with Knut.
"Knut is not like my child and he does not arouse the kind of emotions I feel towards my children," he said in an interview. " For me, Knut is always an animal."
Similarly, Berlin Zoo yesterday categorically ruled out suggestions that Knut would experience feelings of loss as a result of his keeper's passing. "It won't be a problem for him," said Klaus Lüdcke, a Berlin zoologist, "Knut has been looked after by a whole team – and for him the most important person is the one who brings the food."