The Grizzly is originally living an isolated existence deep in the wild, until humans begin to encroach upon his territory, prompting him to go on a rampage.
The Grizzly was portrayed by a bear called Teddy.
At the beginning of the film, The Grizzly stalks a pair of female hikers. He ambushes and kills one of them, while the other flees and finds apparent safety inside a cabin. However, the bear tears down the cabin's wall and mauls the girl, killing her. The bear buries the partially devoured body of the first girl, but leaves the second girl's mangled body inside the destroyed cabin. Later, the Grizzly ambushes and kills a female ranger while she is soaking her feet in a stream.
Later, the bear heads down into the lowlands. He then attacks a campground at night, ripping down a tent and killing a woman. The Grizzly then disappears into the darkness.
After this attack, a bounty is placed on the bear's head and a group of hunters are let into the park. The Grizzly stalks and chases one of the hunters, but he manages to escape the huge animal by jumping into a river and floating to safety. Later, the hunters find a bear cub and, suspecting it to belong to the killer Grizzly, decide to use it as a trap for the mother. However, the Grizzly finds and eats the cub without the hunters noticing. Scott concludes from this that the bear must be a male, as when it comes to bears only the males are cannibalistic. The head park ranger, Kelly, then tells his fellow ranger, Tom, to take watch in a small watch tower. However, the Grizzly manages to sneak to the tower without being seen and then tears down the structure, killing Tom. The bear then disappears without taking Tom's body for food, possibly leaving his body for display as a warning to the other rangers.
Later, the Grizzly attacks a house on the outskirts of the park, maiming a boy and killing his mother. Kelly, Scott and Don, then go after the elusive bear. Don and Kelly kill a stag and attempt to use it as bait to trap the bear. However, the Grizzly sees through the ruse and pretends to retreat, tricking the rangers into following him. The bear then circles back, takes the deer carcass and disappears again.
The next day, Scott, tracking the bear on horseback, discovers the partially eaten deer carcass and attempts to use it as bait to lure the Grizzly towards Kelly and Don. However, the Grizzly ambushes him, killing his horse and knocking him out cold. The bear then covers the injured Scott with a shallow grave and leaves. Later, Scott wakes up and struggles free of the grave. However, as he gets up, the Grizzly reappears and kills him. After this, Kelly and Don, saddened and enraged by their friend's death, decide to continue hunting the Grizzly from their helicopter. They spot the bear from the air and notice that he is returning to the scene of his first kill. They pursue the bear, and though the huge creature manages to keep ahead of the helicopter, the chase appears to tire it out and they land in a clearing.
However, once the helicopter is on the ground, the Grizzly attacks it, swiping it and causing Don to be thrown clear. The bear attacks Don and kills him by crushing him in his forearms. The Grizzly then turns on Kelly, but before it can reach him, Kelly shoots him with a bazooka, blowing the Grizzly to bits and killing him.