Dr. Sporis von Fungenstein
From the Super Mario Wiki
Dr. Sporis von Fungenstein was a Goomba mad scientist and the primary antagonist of the book Doors to Doom. He had built a device that created doors from one world to another. His plan was to take over the world (and become indecently rich) by turning the inhabitants of the Mushroom Kingdom and Koopa clan into mushroom and turtle soup in a chain of fast food restaurants. He had supposedly disposed of everyone who could have stopped him except Mario and Luigi, who he trapped in a series of worlds based on some of their earliest game appearances.
In reality, von Fungenstein worked for the Royal Academy of Mushroom Science and was not a villain at all. Every few years, the RAMS gives out an award for outstanding heroism, bravery, ingenuity, moral character, and overall good looks, and he had engineered the adventure to test the Mario Brothers' worthiness to receive it.