it might be the breed….

Its what they didn’t do. They didn’t communicate to the dog that his behavior is unwanted.

The dog is not the problem, he has instinct to protect his pack.

Pack members

By the sounds of it, the dog is pretty protective of it’s owner! Your friend could lock him in another room when company comes over. And your friend seems to be like the alpha dog to it so that might explain the behavior……..

Sounds like the dog is being protective over your friend. Your friend needs to make himself alpha so the dog realizes that he can protect himself and doesn’t need his help.

Some dogs, either by breed or as individuals, can just be one person dogs. It could also be his upbringing. Perhaps he’s been taught to be protective purposefully (though if your friend has no control over his behavior, the dog is not really trained) or learned through experience that only your friend can be trusted and everyone else is dangerous. There’s no way of telling without knowing more about the dog’s background.

persons fear
natural instinct
loyalty

Dogs will pick their “person” and they will defend that person. That’s their job.

The dog can be trained to accept all people but it will take the time and interest of the “person” who is being protected and he should do that or someday the dog will hurt someone.
He could have the approaching person have some treats and when they approach calmly offer treats to the dog and if the dog stays calm he get praised. Soon the dog knows that approaching people are not a threat, but often come bearing gifts. It will take a while and some repeating, but is easily done.

Some breeds are very protective over their master. Others are friendly towards everyone.
Then there are breeds like the Chow, who will pick one family member that they are close to and the rest better look out.

Some dog breeds are dependant on one person or group of people. Just like a siamese cat has one person that it loves. just try going places with its family more and he should warm up

called a one owner dog. Loyalty. seen it alot with female dogs more than males. Males are much more protective of territory and females of individuals.
Love , jealousy, etc same emotions humans have.

umm for some dogs it might be a special trait but other dogs will protect you if you spend the most time with it and the dog has to knowthat your protecting him (((or her))) but yeah and that ishow some of the dogs i see got that way