In the Nicomachean Ethics Aristotle is primarily concerned with what constitutes the good life for human beings. His moral theory is an example of what is called virtue ethics. This is a school of ethics which emphasizes the individual's character in evaluating moral actions and behavior. The fundamental question for Aristotle is what it takes for an individual human being to be a good person and how character fits into this.
According to Aristotle, everything in life has a function, an ultimate purpose, and this applies equally to each human being. The function of each human individual is to achieve the good life. In relation to that function we need to look at the individual virtues—or moral excellences, such as prudence, courage, temperance, generosity, and so on—and how they are exemplified by our characters in order to see how they fulfill that ultimate function. So the greater the degree of virtue, or moral excellence, we display in our actions, the more adequately we will fulfill our function as human beings.