Greatness

Is greatness born, or made?

There are probably a lot of interesting textbook answers to this, but given that I haven't taken any psychology or many social science courses, I'm idly wondering how much evidence there is in either direction.

More specifically, though, I'm wondering if one is possible even if the other is the "default".

Another way to state what I'm wondering: how immutable is personality? Could a person chemically manipulate his or her physiology to a point where they can build something from a "blank slate" sort of state (or chemically create certain dispositions), or do chemicals merely numb away certain extremes? Aside from chemicals, does attitude or mental drive really accomplish anything in terms of changing a person's "core" set of personality traits?

I know that answering any of those probably gets into philosophy, and that I'm not asking or wondering anything here that hasn't been asked or wondered by many (if not a vast majority of) people before. Still...I think they're all worth asking, and any perspectives are welcome. :-)