Final answer:
In mythology, Adonis is killed by a boar, which Venus had warned him against hunting.
Step-by-step explanation:
In the mythological story regarding Venus's warnings to Adonis, the animal that kills Adonis while he goes hunting, contrary to Venus's advice, is a boar. Venus warned Adonis of the perils he might face should he go hunting dangerous animals. Adonis, refusing to heed her cautions, unfortunately, meets his demise at the tusks of a fierce boar, thus fulfilling the tragic prophecy that Venus feared. This myth is significant in classical literature and has often been referenced or depicted in various artistic and literary works throughout history.