They're even a key part of human evolution:
The dog (Canis familiaris when considered a distinct species or Canis
lupus familiaris when considered a subspecies of the wolf) is a
domesticated carnivoran of the family Canidae. It is part of the
wolf-like canids, and is the most widely abundant terrestrial carnivore.
The dog and the extant gray wolf are sister taxa as modern wolves are
not closely related to the wolves that were first domesticated, which
implies that the direct ancestor of the dog is extinct. The dog was the
first species to be domesticated, and has been selectively bred over
millennia for various behaviors, sensory capabilities, and physical
attributes. Their long association with humans has led dogs to be
uniquely attuned to human behavior and they are able to thrive on a
starch-rich diet that would be inadequate for other canids. 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".