The zookeeper who gained fame for hand-rearing the famous polar bear Knut has been found dead in a Berlin apartment, police said Monday.

Thomas Doerflein was found dead Monday afternoon but authorities had no information on the cause of death, a police spokeswoman said. Doerflein was 44 years old.

He gained fame in Germany and beyond in 2007 as the personal caretaker for Berlin Zoo's most famous resident — Knut the polar cub.

Knut became a sensation when the zoo decided to hand-raise him because he had been rejected by his mother. Doerflein was inseparable from the growing polar bear and often frolicked with Knut in his enclosure. But in July 2007 the zoo's director banned Doerflein from playing with Knut because the bear had grown too large.