"The zookeeper who gained fame for hand-rearing the beloved polar bear Knut was found dead in his Berlin apartment on Monday," according to AP.
A spokeswoman for Berlin police said Thomas Doerflein was dead when authorities arrived at the apartment and that they had no information on the cause of death.
He was 44 years old.
Doerflein worked at the zoo for more than 25 years. According to the newspaper Die Welt, Doerflein was a Berlin native with two grown children. He lived with his girlfriend and her young son.
Update: A statement from Berlin prosecutors said Doerflein suffered a heart attack and that "other causes of death, in particular involvement by another party, are ruled out from a medical point of view." [The Press Association]