not implying that this is how/where/why you got him or he was bred but I have heard of bullmastiff x pit, rottie x pit etc in disreputable breeders claiming they make far more aggressive guard dogs, and some claiming they make better fighting dogs.
just to point out, none of us know anything except that the original poster got the dog/puppy from a breeder. for all we know "breeder" could be a very generalized term in this case, referencing someone who simply owned a female and although its irresponsible they may have "accidentally" let her get pregnant.
the original poster didnt say how much the puppy cost or if it cost nothing.
even if the breeders purpose was to make money by selling these mixed breeds as better guard and/or fighting dogs...I get a strong impression that this owner (original poster) is a great owner.
sorry, just had to say that because some of the replies (mine and others) could be mistaken as looking down at you for getting a mixed breed from a breeder. hopefully we can avoid any comments that would be rude without mistaking their intentions.
gorgeous boy.