The Master is the ruler of the Mushroom Kingdom in around the year 3000. He talks a lot about his kingdom and sometimes sings. He is a really worrier, and is not courageous. His appearance is a tall, slightly fat man wearing a long gold coat that covers most of his face except his eyes. His eyes are bright yellow, and it seems like his skin has a shine to it. On his head he wears a small Toad cap with yellow spots.
When Mario, Luigi and Peach are forcibly taken to his room, he is delighted at the new guests. He brings them on a grand tour, then sings a song about his room. Mario and Luigi walk out first. They walk around a bit when Peach gets attacked by a Dark Figure. When The Master hears about the Dark Figure, he actually faints about what would happen to the Mushroom Kingdom.
Once Mario collects the first Rainbow Sphere, The Master wakes up. He is not much of a help from then on, and spends his time worrying about the Dark Figure.
However, once Mario collects 80 Rainbow Spheres, the Dark Figure is clear enough to reveal it's true form, The Master. It is revealed he had been posing as the king of the Mushroom Kingdom to drill deeper into it's core, where he says holds the creation of all time. Although, this has been causing glitches in time, like creating the portal that brought Mario to that time.
After a long battle, Mario defeats The Master. When he gets back to The Master's room, he finds a princess, called Princess Cherry, hidden in the wardrobe. She is the decendant of Princess Peach and the true ruler of the Mushroom Kingdom. The Master used his powers to turn her into a doll and hide her in his wardrobe for around 20 years, as soon as she was born. He then captured the throne through bribes and magic.