Doctor Faust may qualify as an even earlier proto-mad scientist. Like Victor Frankenstein he is more of a tragic figure than a villanous one, but he is driven by an obsessive desire for knowledge, and eventually this brings him to commit evil acts (not just making a bargain with the Devil, but what he does afterward). According to Wikipedia the earliest known written version of this story dates to 1587. I think this is about as far back as one could plausibly go in Western literature, considering that the first European historical figures who considered themselves to be scientists, good, evil, sane, mad, or otherwise, date to the late 1500s.
I don't personally know of any, but I would not be surprised if an earlier example could be found among the legends surrounding Eastern alchemy.