Caucasian mountain dog.
https://www.bing.com/images/search?q=full%20grown%20caucasian%20mountain%20dog&qs=n&form=QBIR&pq=full%20grown%20caucasian%20mountain%20dog&sc=1-33&sp=-1&sk=
The Russians use these in their prisons. It states you have to know these types before having one. Ya think!
Chief looks like this, but a little bigger because his old man was a 250 pt St. Bernard.
http://dogsarena.net/blog/2015/03/03/fila-brasileiro-the-most-versatile-mastiff-breed/
They resemble bears.