Montmorency

Montmorency is the narrator's fox terrier from the novel Three Men in a Boat by Jerome K. Jerome. He accompanies the three titular hypochondriacs in their jaunt down the Thames.

George in "Three Men and a Vampire"
Although it is well known that Montmorency accompanied the Three Men in their more famous, mundane misadventures, it is somewhat lesser known that he also accompanied them on at least one brush with the supernatural.