Both Immanuel Kant and Aristotle are major ethical thinkers who have greatly influenced the western intellectual tradition. Each have made unique and important contributions.
Aristotle is important for his treatment of eudaimonia, or human thriving. His notion of the good is based on the relationship of the individual soul to the situation of the person within the community. He especially emphasizes that although the ultimate good must be something desired as an end rather than a means to an end, a point that is a good counter to the crude materialism of much of modern society.
Kant is most important for his notion of moral autonomy and how an ethical act must be willed as such. He contributes rigour in his treatment of meta-ethics and the foundations of ethical reasoning. His deontological bent leads him to function to a major limitation of naive consequentialism, namely that we must often act when we cannot accurately foresee the consequences of our actions.