He was a Geki warrior and unusually large for a wolf.
Ginga Nagareoboshi GinEdit
Ben was stronger than him (despite being smaller) and gave him a chance to live. He told the wolf not to use the title of the Geki warrior anymore, since he believed that Mukonga was the true Geki warrior.
However, Bighorn didn't listen to him and tried to attack the Great Dane from behind, claiming to be the true warrior. Angered, Ben killed him with one blow.
See more pictures in Bighorn/Gallery