Aristotle was a student under Plato, and although he did not believe in the metaphysical Forms that Plato so firmly believed in, he did apply an element of the theory behind the Forms. Instead, what Aristotle postulated was that there was some ultimate, some final goal to which we all reach, but instead of being some unattainable goal, it was very simple: happiness. Happiness manifests itself in all of our actions, whether it's a conscious process or not, but when we are truly happy is when we do things that are virtuous and honorable. And instead of being some latent part of another goal, Aristotle stated that happiness was the goal, that there was no higher form to achieve beyond.
In chapter seven of Book One, Aristotle is almost vague as he tries and defines what happiness is, and more importantly, why happiness is crucial to the human function, and in fact states that "nor should we demand to know a casual explanation in all matters alike" (1098b). Comparing it to simple truths that are a priori, like when dealing with fundamental principles, he admits that it cannot be defined so easily nor so quickly. He then struggles, in chapter eight, to define happiness. It is, according to him, a kind of "good life and well-being;" virtue precludes action as well as thought. It is also synonymous with virtue: even though virtuous acts are, in general, "not pleasant by nature men who love what is noble derive pleasure from what is naturally pleasant" (1099a).
Aristotle also makes a clear separation of happiness that is god-given makarios and a happiness that is produced through human effort and virtue, eudaimon.
But it seems as if there is an inherent flaw in his outlook for those who are not blesses with makarios and