What kind of animal is often referred to as "man's best friend"?

Dogs are often referred to as "man's best friend." Through the ages, people have claimed dogs as one of their closest and best companions. Of all the domesticated animals, dogs serve the widest array of roles: protector, helper, lifesaver, and companion. Dogs are incredible friends to people and they've been companions through centuries. The relationship between dogs and people is deep and old.

Source: Rover.com