He was owner of GB.
Ginga Densetsu Weed
He was shown in GB's flashback in the beginning of the story where GB used to live in a happy life as a pet dog with his owner. However, the happy life was shattered when the owner was involved in the money debt and he tearfully chased his dog away by lashing him with a leash before hanging himself. Then, when GB came back and found his body, the ambulance had also arrived and took the body away that GB chased after the ambulance without realizing that there are other vehicles on the road which caused the dog to almost get run over on the road if not for Smith's intervention (which saved GB's life and had cost Smith's leg).
He died of an unknown cause before the beginning of the series so he is only mentioned.