Aristotle (384 to 322 BC)
I believe that Aristotle is the one who has contributed most to the fact that subsequent philosophers have not seen the basic idea. Firstly, following Plato, equals the good of man with the good of the City or the State. But as it seems to him a very ideal idea and also does not "see" the State as subject, he considers men to be subjects, every man. This election "homoegophilic" (Forgiveness for the neologism) will sacralize individuals in front of the community. And it is on the "rational" basis of all Western ethics until today. Against the intuitive norms, familiar and tribal, of the previous societies.
Aristotle will seek the purpose of Man in every man. He wonders what each man wants. And he concludes, rightly, that all men want happiness. And he deduces that Happiness is the supreme Good. That being happy is the goal or goal of men. And he takes it to another level and Happiness becomes the Good of Man.
On the other hand, Aristotle, despite his knowledge as a biologist, does not even think that Man can become extinct and less able to do something that leads to his own extinction. The ethical norms, which had been mostly laws directed to individual and group self-preservation, become moral norms, "spiritual" norms. And from being material commandments, they become moral virtues.
Aristotle does not come to discover what is the happiness to which we all tend. Nor what is the main virtue for trying to get it. But he began the practice of seeking the foundation of ethics in individuals, who are, for him and for all philosophers, the ethical subjects. Which is true. But it is not the individuals who have said, nor can say, what is the Good of Man, of Humanity, nor of the men themselves as members of humanity. It is as if a soccer player is asked what his personal goal is. He will say that to earn money and fame. But that is not his purpose as a player. His purpose as a player matches that of the team he is part of: winning the matches. That is Aristotle's mistake.
For Plato the Good was primary the good of the State, which usually coincides with the welfare of the citizens. For Aristotle, the primary good was the indefinite happiness of citizens. Without realizing that, in order for citizens to be, they need a society, a State. And for being happy the virtue to practice individually is fair coexistence, extended altruism, collaborating so that the rest of the citizens have the greatest possible welfare. Which is the best strategy for a strong and sustainable State to exist.
Aristotle, with all his wisdom, did not know how to see the Man as a subject and consecrated individualism. Which has been excellent for intellectual and technical progress but has hidden reason the priority objective of Man as humanity, as Sapiens. I believe that this is the main point of why later philosophers and theologians continued to see men only as individuals, without realizing that they took away their main quality: that of being part of a team whose primary vital purpose is to conserve and transmit -until who knows when and why- the life they have in their hands.
In any case, it seems that Aristotle, besides being wise, was a well-intentioned man. My best memories. And possibly we are still in time to rectify.