Writes philosopher Greg Salmieri on the differences between Ayn Rand and Aristotle at Check Your Premises blog:
Rand is always focused on the individual human being, who has distinctive ideas and personal values that set him apart from others in his community and that may put him in conflict with them. She presents her moral philosophy in explicit contrast with moral codes that call for the individual to sacrifice his ideas and values to the demands of others. And, likewise, her political philosophy is formulated in explicit opposition to political philosophies that justify the sacrifice of individuals by the state. In this respect Rand has more in common with 19th Century individualists like Max Stirner and Friedrich Nietzsche than she does with Aristotle. This individualism is also characteristic of the Romantic movement in literature, which Rand saw herself as a part of. All of these individualistic thinkers extol emotions (and/or will) as the seat of individuality, whereas Rand identifies a person first and foremost with his reason. In this she agrees with Aristotle, but her view of reason includes elements that were absent or under-emphasized in Aristotle.
Whereas Aristotle’s discussions of reason’s role in life are impersonal in character, Rand held that an individual’s reasoning is the source of the personal values (e.g. his love of his job or romantic partner) that make his life meaningful to him. This is because, in her view, reason is an attribute of the individual and it does not function automatically. Each individual must initiate and sustain reasoning by choice, and must learn how to discover knowledge and to choose values that are based on facts and integrate into a self-sustaining life. To function in this manner by choice is to be objectivein Rand’s sense of this term. I elaborated on this point in Chapter 6 of A Companion to Ayn Rand:
Only insofar as an individual chooses values in this way does he have a self‐interest at all. Values chosen subjectively, without regard for the requirements of human survival, will not form into a self‐sustaining whole; so rather than a coherent self‐interest that he can act to advance, the individual will have a motley assortment of conflicting desires. But neither can self-interest be intrinsic: there is an inexhaustible variety of possible combinations of values and activities that could cohere into a self‐sustaining human life, and there is nothing other than an individual’s choosing and pursuing one of these possibilities for himself that can make this particular life constitute his self‐interest and ultimate goal.