"Man's best friend" is a common phrase about domesticdogs, referring to their millennia-long history of close relations, loyalty, andcompanionshipwithhumans. The first recorded use of a related phrase is byFrederick the Greatof Prussia. It was likely popularized by its use in a poem byOgden Nashand has since become a commoncolloquialism.
Before the 19th century, breeds of dogs (other thanlap dogs) were largely functional. They performed activities such as hunting, tracking, watching, protecting and guarding; and language describing the dog often reflected these roles. According to theOxford 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 therabies vaccinein 1869.