Which myth's central narrative features an animal that is entirely antagonistic toward the hero?

The central narrative featuring an animal that is entirely antagonistic toward the hero is rooted in the story of Theseus and the Minotaur. In this myth, the Minotaur, a monstrous creature that is part man and part bull, serves as the primary antagonist. It resides in the labyrinth, an elaborate maze designed by Daedalus, where it preys upon the youth of Athens as a form of tribute demanded by King Minos of Crete.

Theseus, the hero of the story, volunteers to go into the labyrinth to confront the Minotaur and ultimately seeks to bring an end to its threat to his city and the lives of the captured youths. This confrontation is marked by the clear opposition between Theseus and the Minotaur, highlighting the Minotaur's role as a malevolent force that must be defeated for peace to be restored.

The other narratives involve more complex relationships where the antagonism may not solely be due to the animal nature of the character or situation, but rather intertwined with themes of heroism, destiny, or transformation, making those relationships less clear-cut regarding a singular antagonistic focus on one creature.