Grizzly bears are pretty large and tough animals so not just any animal could kill or eat a grizzly bear.
Grizzly bears can usually defend themselves and kill other potential predators.
However some Grizzly bears have killed Grizzly bear cubs which are smaller than the adult grizzly bear.
Grizzly bears do not really have any natural predators that will attack them for the food but if a Grizzly bear gets into a fight with another animal such as a Wolf then the wolf may be able to attack and kill the grizzly bear.
There have been times where several wolves came up against 1 Grizzly bear and the pack of Wolves was able to overpower the grizzly bear and kill the Grizzly bear.
Of course any large amount of animals that come up against just 1 grizzly bear could easily kill or at least injure the bear.
Bears though including the Grizzly bear are pretty tough and powerful animals themselves.