Full Idea
Socrates' true place in the development of Greek thought is that he is the first to establish the eudaimonist foundation of ethical theory, which became the foundation of the schools which sprang up around him.
Clarification
'Eudaimonist' means concerned with a happy, or fulfilled, or successful life for the individual
Gist of Idea
Socrates was the first to put 'eudaimonia' at the centre of ethics
Source
report of Socrates (reports of career [c.420 BCE]) by Gregory Vlastos - Socrates: Ironist and Moral Philosopher p.10
Book Reference
Vlastos,Gregory: 'Socrates: Ironist and Moral Philosopher' [CUP 1992], p.10
A Reaction
I suspect that he was the first to fully articulate a widely held Greek belief. The only ethical question that they asked was about the nature of a good human life.