Which author's Foundation series shaped science fiction?

Asimov, who began it at 21 and built it on an idea borrowed from Gibbon - the Decline and Fall of the Roman Empire transposed to a galactic scale, with a mathematician who can predict the behaviour of vast populations statistically while remaining unable to predict any individual.

That invention, psychohistory, is the series' whole argument: that history has laws at scale even if people are unpredictable one at a time. It is also a proposition social science has spent eighty years failing to deliver on, which does not seem to have dented its appeal to economists and to a certain kind of technologist.

Asimov also gave the field the Three Laws of Robotics, and the interesting part is that almost every story he wrote using them is about how they fail - ambiguity, conflicting instructions, harm that is indirect. They were designed as a plot generator rather than a safety proposal, which has not stopped them being cited in earnest in AI ethics discussions ever since. He wrote or edited something close to 500 books and had a Dewey Decimal entry in nine of the ten main categories.