This is a good question. In order to answer your question, I have to go back to two philosophers - Heraclitus and Plato. Heraclitus argued that all was in flux. He famously said that you cannot stand in the same river twice. Plato tried to solved his problem of flux by arguing that there were eternal forms. So, there might be many tables in the world with great variety, but through dialectics, a person is able to get to the eternal form of a table - the perfect form of a table.
Now Aristotle came along and tried to take another step forward. He bridged the gap between Plato and Heraclitus. He argued that there was change but even within these changes there is always something that stays the same. A person is able to find what things have in common through astute observation.
Now we have to define metaphysical realism. Metaphysical realism, in a nut shell, states that the world exists independently of how humans take it to be.
In light of this definition, Aristotle was one of the essential figures to create metaphysical realism.
His works were lost for a time, but were rediscovered with contact with Muslims. They they were reintroduced into the West. When this happened these translations formed the basis of the commentaries of Albert the Great, Thomas Aquinas and Duns Scotus. This work made a profound impact on Western philosophy.