Mary Allen
#4 Mistreatment
The cause could be that your Golden Retriever has been mistreated in the past. If this is the case, it could be that he sees strangers as a threat. He reminisces and fears that something similar to what happened in the past will happen. When you adopt a dog from an animal shelter or from abroad, you don't know what he has experienced in the past. But don't worry, even then you can do something to make it better.
#5 The unwanted behavior was reinforced
You may also have encouraged your golden retriever to do this by giving him attention - e.g. petting, hugging, talking - when he barked at a stranger.
Don't pay attention to him when he's misbehaving. Notice when he's about to bark and try to redirect his attention. You can use this method not only for barking but for any unwanted behavior from your dog.
#6 Teach him to associate other people with rewards
The first option would be to teach him that other people are associated with a reward. On a walk, feed your golden retriever treats when you approach a stranger. As soon as he starts barking, stop giving him treats. Only when he's calm and focused on you do you reward him again. He learns that barking is punished with the withdrawal of treats.