English Mastiff

Dog

The English Mastiff, referred to by most Kennel Clubs simply as the Mastiff, is a breed of large dog perhaps descended from the ancient Alaunt through the Pugnaces Britanniae. Distinguishable by enormous size, massive head, and a limited range of colors, but always displaying a black mask, the Mastiff is noted for its gentle temperament.

http://en.wikipedia.org/wiki/English_Mastiff