We are generally all familiar with that doggy smell. It's unsurprising dogs smell considering they go exploring in muddy puddles and undergrowth when on long walks, and only have a wash about once a month. Your dog may smell bad because he has rolled in something smelly like cow poo or he may be suffering from gas.
A pug lying on the floor indoors waiting for its owner to return
If you wash your dog regularly you should be able to combat that doggy smell. Infections of your dog's ears, mouth or anal glands can also cause bad smells. If you suspect the cause of the smell might be infection you should contact your vet to get him looked at.