Diefenbaker is Constable Benton Fraser's deaf Arctic wolf who follows everywhere and helps Fraser with his investigations.
Also known as "Dief," Diefenbaker is commonly mistaken as a dog although Fraser often points out he is half wolf and half "well, he doesn't know what the other half is." Diefenbaker was named after Canada's 13th Prime Minister John Diefenbaker. He came to live with Fraser of his own free will after pulling him from the Prince Rupert Sound's icy waters in 1992. Although this resulted in the wolf's apparent deafness as his eardrums burst from the cold, he can still read lips in English and Inuktitut which leads to public conversations with Fraser, resulting in Detective Raymond Vecchio's great embarrassment.
Diefenbaker is very loyal to Fraser and although they occasionally give each other the cold shoulder, the wolf has followed Fraser everywhere including Chicago where, to the constable's despair, he has become much of a city dog, developing a taste for fast food and even has his own checking account, which Fraser is careful to never disturb.
Diefenbaker has been known to attack others to protect Fraser and when they are in trouble, the wolf always seems to find a way to save them. Diefenbaker has had several run-ins with animal control, but Detective Vecchio forged a "wolf permit" that would allow him to stay in the city. During his first months in Chicago, the wolf often stays in the apartment with his minder Willie, a twelve-year-old purse snatcher, until he escapes one day and is almost put to sleep for not only biting an animal control officer but also Fraser. It is later discovered that there is an illegal operation running from the animal control office; Diefenbaker ends up saving the lives of numerous other dogs, including his own pups, two of whom are named Buster and Sunshine.
Diefenbaker received the first fan mail for the series and was even parachuted out of a plane as a member of the RCMP. The wolf was portrayed by six similar-looking Canadian Husky dogs, Lincoln, Frankie (Pilot only), Chinook, Kerry-Ann, Draco and Cinder (Draco's sister who performed most of her brother's stunts).