What mythical monster was killed near Mount Parnassus by Apollo at the site of the Delphic Oracle?

The mythical monster killed near Mount Parnassus by Apollo is known as Python. According to Greek mythology, Python was a serpent or dragon that guarded the oracle at Delphi. Apollo, seeking to claim the site for himself and establish the Delphic Oracle, confronted and defeated Python in a fierce battle. This victory not only demonstrated Apollo's strength and divine authority but also paved the way for his worship and the establishment of the famous oracle.

In the context of the question, Python's defeat is significant as it marks the beginning of Apollo's association with the oracle and his role as a deity of prophecy. This event also illustrates the themes of conquest and the establishment of order over chaos, which are prevalent in many myths surrounding the establishment of sacred spaces in ancient Greece.