The dog (Canis familiaris when considered a distinct species or Canis lupus familiaris when considered a subspecies of the wolf) The dog and the extant gray wolf are sister taxa Dogs vary widely in shape, size and colors. They perform many roles for humans, such as hunting, herding, pulling loads, protection, assisting police and military, companionship and, more recently, aiding disabled people and therapeutic roles. This influence on human society has given them the sobriquet of "man's best friend".