A good "X" is an X who x's well. Where x'ing is to perform the function of x.
So. What is a good human? A good human is one who performs/fulfills the human function well.
The obvious question is, what is the human function?
An objects uniqueness is an indicator of function. Aristotle determines that reason is the uniqueness of humanity.
Man is "the rational animal" The animal with logoV.
Man's function then, is rational activity.
Man is the "rational animal"