The panserbørne (literally "armour-bears" in Danish) are based on polar bears, which are native to the Svalbard in our world and have become the islands' symbol and primary tourist attraction.
The polar bear is the world's largest land carnivore, with adult males growing up to 680 kg. Their fur is in fact clear and their skin black, but due to the thickness of the fur it appears white, allowing them to blend with their habitat. The fur sometimes yellows over time, suggesting Iorek is not a young bear.
Polar bears are far less territorial than other bears, and tend to be more cautious when confronted. However if they are hungry they can be unpredictable and have been known to kill and eat humans.
They are classified as "vulnerable" in conservation terms, because of the rapid depletion of their habitat due to the melting of the Polar ice caps.