"Before" you shampoo him, use a slicker brush to get all the tangles out. Water down the shampoo so it isn't so strong. Use a really good conditioner and mix in some vegetable glycerine. His hair is really dry and is why he's matting so much. Blow dryers are terrible at drying the hair too, so make sure you always use lots of conditioner. After the coat is dry, you can add some Pet Silk Liquid Silk. It's what I use on my girls and it's amazing stuff.
PetSilk Liquid Silk - PetSilk Products