No one really knows who Pop Fizz was before he became an alchemist, least of all Pop Fizz himself. After many years of experimenting with magic potions, his appearance has changed significantly. In fact, no one even knows its original color.
But everyone knows that he is a little crazy, that his experiments are imprudent and that the accidents they cause are too numerous to measure.
Naturally, he had difficulty finding lab partners, or anyone willing to be near him. Hoping to make himself more attractive to others, he attempted to create the most effective charm potion ever created - but it simply turned him into a large, savage berserker. Or maybe that's just how he saw the potion working in the first place...