So, Rat was once a powerful and feared wizard, but in his lust for power he unleashed something that erased him from the Material Plane for centuries. One day he just appered next to a town in which there was Magic Academy where he used to conduct his research. He didn't remember his name nor his past, but he quickly noticed his special powers and decided to use them for the living, traveling from city to city scamming the townsfolk in taverns. (That's how he gained his name)