First, use some type of a dematting tool to remove the mats as best you can. Clippers won'tcut through the mats well. Then use a high quality clipper (i.e. Andis Golden A5, or similar). I believe the Waube clippers tend to be quieter than the Andis, so you may prefer them. Use a #7 skip tooth blade for the jacket, a #9 for the head, ears, throat, shoulders, belly and buttocks. If you don't comb/brush him regularly, which seems to be the case since he is matted, use a #4 blade on the legs and face. Fluff up the leg hair and use a scissors to even it out.
Once he is clipped, start brushing him at least once/week with a wire brush (ball tipped wires) and combing him out with a steel comb. If you invest in a Coat King rake, that will help to control the undercoat and keep him from matting as well.