Molecule Man is another one of those scientists who messed up in the lab and got powers because of it. His powers are to manipulate the atoms of inanimate objects. I guess whether you become a good guy or bad guy after that all depends on what influences you have in your life. Molecule Man was in a very negative place when he got his powers, so he went the villain route instantly. His first action was taking over the Fantastic Four's building and declaring himself ruler.
The Fantastic Four couldn't beat him at first, but then after realizing that he could only control inanimate objects, they hid themselves in statues. When olecule Man tried to manipulate the statues, it hurt his brain and they beat him. That was only the first time he started trouble though. It never is.