Grizzly bears have no natural predators. Sometimes wolves and grizzlies will fight over a kill, and sometimes pumas and grizzlies will fight over a kill, but the larger grizzly will generally win without much bloodshed as the pumas and wolves are smart enough not to pick a serious fight with a grizzly.
Jaguars would be the only cat that would have been a threat to a grizzly bear, but thanks to humans their ranges no longer overlap 🙁 so we don’t know much about what what would happen were a grizzly to encounter a jaguar in the wild.
Tigers have been known to attack other brown bear species, but tigers are native only to Asia and grizzlies only to North America. And a tiger would be more likely to attack and eat you than a grizzly.