Martinez picked the Cordoba Fighting Dog to be the base for the breed. The breed is extinct today but was described as a large and ferocious dog that was both a great hunter and fighter.
With the Cordoba Fighting Dog as the base, he then crossed in Great Dane, Boxer, Spanish Mastiff, Old English Bulldog, Bull Terrier, Great Pyrenees, Pointer, Irish Wolfhound and Dogue de Bordeaux.
Martinez kept improving the breed via selective breeding to introduce the traits that were desired. The first standard for the breed was written in 1928.