Gray Wolf is an icy breed of Tiger with a ??? sub-type, but its gray color leads one to believe it may have a Zain connection. It is exclusive to Monster Rancher 1 and Monster Rancher Battle Card 2, and as a non-playable monster in Monster Farm Online.
In the anime series, Gray Wolf is Tiger's brother, who was kidnapped by Moo at a young age and turned into one of his top lieutenants. Gray Wolf eventually has to face Tiger in a battle and come to terms with all of the damage he has caused.
Monster Rancher 1: He has a beautiful coat of silver fur and howls at the night.
The grey wolf is an actual animal. They mostly live in North America and hunt in packs.