The Mongolian Mastiff is actually the Tibetan Mastiff. It is also referred to as a banhar, or "four-eyed dog" in Mongolian. The Canis lupus hominis site notes that the name four-eyed dog came from the tan coloring above the eyes, which looks like another set of eyes.
The American Kennel Club has classified the Tibetan Mastiff in the working breed group, noting that it is very protective of family and property. Some breeders differentiate this mastiff into two types: the Do-khyi and the Tsang-khyi, the latter generally considered to be taller and more heavily boned, with increased facial wrinkling and haw.