Aristotle was a philosopher, teacher (he tutored Alexander the Great), scientist, astronomer, and political theorist who dominated the world of knowledge like no one before him or since.
He is also credited with inventing logic and was the first to divide human knowledge into separate categories enabling us to understand the world in a systematic fashion.
Aristotle steered away from Plato's realm of forms and was not inclined to dismiss the world around us as unreal. Where Plato considered reality knowable only through reflection and reason, Aristotle saw it in physical objects, and knowable through science.
Aristotle is said to have transformed every field of knowledge that he touched (except for mathematics where Plato and platonic thought were supreme). He studied, wrote about, and became an expert in every field of science including anatomy, physiology, physics, geology, geography, and astronomy.
Often regarded as the father of psychology, Aristotle is also believed to have contributed more to psychology than any other person. His book De Anima (On the Soul) which deals with the connection between psychological and physiological processes is considered to be the first book on psychology.
Aristotle's influence did not stop there. Whether in science or government he was a visionary who understood how everything worked.
Regarding the concept of democratic government he said: "Man is by nature a political animal. The basis of a democratic state is liberty. If liberty and equality are chiefly found in democracy, they will be best attained when all persons alike share in government to the utmost."
His work Nicomachean Ethics which focuses on the importance of virtuous character and ethical behavior is among the most influential treatises on morality ever written.
Another key concept of Aristotle's was The Golden Mean - avoid extremes, moderation in all things.
The scope of Aristotle's work is immense and his influence has been immeasurable. The potency of his philosophy, metaphysics, logic and ethics remains unimpaired.