Big Tibetan Dog - Tibetan Mastiff

What is the world's biggest dog ever?? have you ever see this big dog before?? this is a Tibetan dog, a very ancient working dog resembling a Newfoundland used as herding dog and caravan guardian and considered the ancestor of all molossers. i don't know what is the specific names of these species, when i search on wikipedia.. i found that the names of this big dog species was Tibetan