Aristotle was a Greek philosopher and polymath who lived from 384 to 322 BC.

Augustine of Hippo, also known as Saint Augustine, was a prominent theologian and philosopher from the Roman province of Africa.

Avicenna, also known as Ibn Sina, was a renowned Persian physician, philosopher, and scientist who lived during the Islamic Golden Age.

The Cappadocian Fathers, also traditionally known as the Three Cappadocians, were a trio of Byzantine Christian prelates, theologians and monks who helped shape both early Christianity and the monastic tradition.

Existence is the state or fact of being present, real, or occurring.

The Wikipedia page on the Universe provides an overview of the vast and complex cosmic entity that encompasses all of space and time.