Plotinus was an ancient philosopher regarded as the pioneering founder of Neo-Platonism, a major philosophical movement of the Graeco-Roman world in late antiquity. He is also known as one of the last and most prominent pagan philosophers. His metaphysical writings have influenced centuries of thinkers, including Pagan, Christian, Jewish, Islamic, and Gnostic metaphysicians and mystics. Plotinus developed a metaphysical system that explained the rational world and the human soul, positing that the ultimate cause of everything is "the One" or "the Good." He described "the One" as utterly simple and beyond comprehension, resisting definition or conceptualization. A devoted follower of Plato, Plotinus considered himself an interpreter and advocate of Plato’s philosophical vision, which he regarded as the highest ideal of philosophy. In addition to significantly influencing Western thought, Plotinus also impacted 17th-century England, medieval Islamic spirituality, and Indian medieval philosophy. His teachings are preserved in a collection of his discourses, compiled and edited by his student Porphyry into six books of nine treatises each, collectively known as the Enneads.