Remember the old D&D Cartoon from the 80s? Six kids are magically transported into the world of Dungeons & Dragons where they fight the forces of evil while trying to find a way home. (See the cartoon intro below). In the cartoon the Dungeons Master was an actual character. He would appear at the beginning of each episode and provide the heroes with a quest; in much the same way the DM does during an actual game of D&D. The DM served as the guide for the characters in the show and the viewers at home. He’d also step in from time to time and give the characters advice or help them out of a really tight jam.
In 4e D&D the DM is not one NPC, rather the DM takes on the roles of every NPC. But wouldn’t it make things easier if Dungeon Master actually was an NPC in your game?