The grizzly bear (Ursus arctos ssp.) is any North American subspecies of brown bear, including the mainland grizzly (Ursus arctos horribilis), Kodiak bear (U. a. middendorffi), peninsular grizzly (U. a. gyas), and the recently extinct California grizzly (U. a. californicus†) and Mexican grizzly bear (U. a. nelsoni†). Specialists sometimes call the grizzly the North American brown bear because the grizzly and the brown bear are one species on two continents.
Due to the Simian Flu Pandemic, human kind had been drastically plummeted by 9 in 10. This allowed grizzly bears and pretty much every form of wildlife worldwide to thrive and expand without human interference. It can be assumed that grizzly bears had began to spread and some made residence within the Muir Woods Park, where they became territorial and competition enemies to the equally thriving colony of apes. The Evolved Apes were able to protect themselves from grizzlies by their self made spears and bolas.
One elk was caught up in a bolas thrown by Caesar during a hunting trip, where it laid panicking before Caesar and his son Blue Eyes ascended to butcher their kill, but after noticing signs of bears living in the woods by some claw marks on a tree, they were interrupted, and Blue Eyes was attacked by a huge grizzly bear, gaining large wounds across his chest and face from its claws. Caesar quickly came to rescue his son by driving his spear at the bear, but out of instinct the bear swiped Caesar's spear away and stood high above them in a sizing contest. Caesar yelled at the bear to try and scare it off while calling for aid and Koba heard his king's calls, rushing through the woods to their aid. As the bear reared to deliver a fatal blow to Caesar, Koba jumped at the bear and drove his spear through the back of its neck, fatally injuring it. The bear's dead body fell to the ground with Caesar beneath, but to Koba and Blue Eyes' relief he was not hurt.
The bear was brought back to the Ape village with the other ape kills for butchering.