Victor, the country's oldest polar bear, has died aged 22.
The animal, which was living at Yorkshire Wildlife Park in Doncaster, had terminal kidney failure and became unexpectedly ill earlier on Friday so vets put him to sleep.
Victor was born at Rostock Zoo in Germany, before moving to Rhenen in the Netherlands.
After he retired from the European breeding programme, he was rehomed in Yorkshire in 2014.
He fathered 13 cubs during his time in the breeding programme.
The park said he "spent his days enjoying the lakes and expansive habitat" at their reserve.
The directors of Yorkshire Wildlife Park thanked the vets who "responded so quickly" after Victor was taken ill.
They also paid tribute to the "dedicated staff who have loved and cared for Victor since his arrival and who today are saddened at the loss of one who was a favourite for staff and visitors alike".
"Victor was a great ambassador for his species, inspiring generations and drawing attention to the plight of his species in the wild and the threat of climate change.
"He will be greatly missed."
Yorkshire Wildlife Park said: "Victor was a great ambassador for his species, inspiring generations and drawing attention to the plight of his species in the wild and the threat of climate change. He will be greatly missed by everyone."
Yorkshire Wildlife Park is home to the only polar bears in England. The only other bears in the UK live at Highland Wildlife Park in Scotland.
