Cross Obi Wan Kenobi with Yoda and you have the weird, weird being that serves as guide of this weird, weird land. Some guide! He's only sometimes there when they need him and, most of the time, he leaves them completely alone to stumble and venture all over the terrain.
The Dungeon Master knows all about this land (so he says) and he's on our heroes' side (so he says). But he has this maddening way of appearing, telling them something they need to know, and then vanishing before they fully understand it. He rushes about, always seeming to be in a hurry, and he'll tell them some vital, important fact about the next leg of their journey or about what they'll encounter over the next hill. Then he'll be gone and they'll be left to wonder just what he meant by what he said. Eventually, of course, they'll find out. Everything the Dungeon Master says has a purpose, even if it takes until the end of the episode to figure out what. But he speaks in ciphers and puzzles and he is constantly leaving them to figure things out for themselves.
He does not just appear out of thin air. Or maybe he does. No one ever sees him appear and no one ever sees him go. For our purposes, he will just suddenly be in a shot and the kids will look down, do a gang double-take and wonder where did he come from. Or, sometimes, they'll open up a door and there he is! He can be anywhere... or nowhere ... with neither rhyme nor even reason.
He doesn't just vanish into thin air. Or maybe he does. The kids will be distracted by something and, when they look back, no Dungeon Master! Gone, just like that! Or he'll lead them into a room and, when they get inside, he's nowhere to be seen. Somehow, he evaporated in mid-threshold.
How he appears and disappear is but one of the mysteries of the Dungeon Master. The kids feel that he knows all the secrets – including the all-important one as to how they can finally get home. Why doesn't he just tell them these things? Why does he make them go through one dangerous situation after another when he obviously could tell them how to avoid these things? Eric especially gets exasperated at the Dungeon Master's cryptic ways -- but they have no answers. All they know is that he is wise, that he seems to be on their side, that following his advice always turns out in the end although it may get very, very hairy along the way; that everything he says has a meaning if you can figure it out...and, above all, that he is the dread enemy of the evil Venger. Perhaps they have even been brought here specifically to combat Venger.
Like the kids, we see little of the Dungeon Master. He pops up from time to time in the oddest places to offer advice, though he never actually solves their problems; in fact, he sometimes seems to complicate matters. In the end though, they understand what he meant, though not always why he didn't just come out and tell them. This odd little man is one of the greatest mysteries in a land that is All Mysteries.
Biography copied from Series Bible.