The wooly mammoth.
It is perfectly adapted to survive ultra cold climates in Siberia. They’ve even done estimates that at least 48,000 of them could survive in Alaska alone today.
They were big, strong, and capable of defending themselves against polar bears.
The problem would simply be with poaching and hunting. Some people would see them as the ultimate trophy to have on their wall.
But a part of me thinks most would relish the opportunity to see these big fellas roaming the earth again.