Dog, A Man's Best Friend

Before the evolution of wolf into dog, it is posited that Man and wolf worked together hunting game. Wolves were the superior tracker but man was the superior killer, thus wolves would lead man to the prey and man would leave some of the meat to the wolves. This working relationship eventually led to the evolution of dogs, although there is controversy as to the exact nature of that transition. Some say wolves evolved naturally into dogs, wherein the wolves that worked best with humans slowly began to assimilate and pass their domesticated genes down. Others say that humans took wolf pups and raised them to be domesticated. Either way, man and dog formed a working relationship.
Previous to the 19th century, dogs, other than lap dogs, were largely functional. Used for activities such as hunting, watching and guarding, language describing the dog often reflected these positions within society. According to the Oxford English Dictionary, “In the oldest proverbs and phrases dogs are rarely depicted as faithful or as man’s best friend, but as vicious, ravening, or watchful.” Beginning in the 18th century, multiplying in the 19th and flourishing in the 20th century, language and attitudes towards dogs began to shift. Possibly, this societal shift can be attributed to discovery of the rabies vaccine in 1869.
The earliest citation of the actual word choice - in English - is traced to a poem printed in the The New-York Literary Journal, Volume 4, 1821: