How was Aristotle important in western civilization?
Aristotle served as the foundation for many aspects of philosophy, science, and theology for a period of over 1500 years.
His first major position of some importance was his role as tutor to Alexander the Great, shaping the mind of one of the most important rulers of antiquity.
Next, he founded the Lyceum and Peripatetic school of philosophy, a role which included training may of the wealthy and famous of his period.
Aristotle was one of the first thinkers to make a systematic study of biology, and attempt to classify plants and animals. His encyclopedic interests are also reflected in his collecting constitutions of the city states of Greece and summarizing and collecting the works of a wide range of earlier thinkers. Without Aristotle, we would have far less information about the history of ancient Greek culture.
Aristotle's scientific ideas influenced much of medieval Arabic and European thought. Scholasticism, a synthesis between Aristotle and Christianity made by medieval theologians such as Thomas Aquinas, dominated much of Roman Catholic theology until Vatican II.