The giant dog in Thor is Fenris, a mythical wolf in Norse mythology, who is depicted as the son of Loki. He is a fearsome creature with incredible strength and a fierce loyalty to his master, Hela, in Thor: Ragnarok.
Fenris's role in Thor: Ragnarok is to serve as Hela's loyal companion and enforcer. His imposing size and raw power make him a formidable opponent, and he is a constant threat to the heroes throughout the film. Despite his menacing appearance, Fenris also exhibits a playful side, displaying a fondness for his mistress, Hela.
While Fenris isn't depicted as a traditional "dog," he acts as a companion to Hela, similar to how a dog would be to its owner. He is a powerful and loyal creature, much like a giant dog, making him a memorable character in the film.
