Question: The Pluralist school was a school of pre-Socratic philosophers who attempted to reconcile Parmenides' rejection of change with the apparently changing world of sense experience, it can also be said to have included which philosopher who was the earliest Greek to develop the theory of atomism—the idea that everything is composed entirely of various imperishable, indivisible elements called atoms. Leucippus often appears as the master to his pupil Democritus, a philosopher also touted as the originator of the atomic theory?
Context: In chemistry and physics, atomic theory is a scientific theory of the nature of matter, which states that matter is composed of discrete units called atoms.  It began as a philosophical concept in ancient Greece and entered the scientific mainstream in the early 19th century when discoveries in the field of chemistry showed that matter did indeed behave as if it were made up of atoms. Zeno's paradoxes are a set of philosophical problems generally thought to have been devised by Greek philosopher Zeno of Elea (ca. 490–430 BC) to support Parmenides' doctrine that contrary to the evidence of one's senses, the belief in plurality and change is mistaken, and in particular that motion is nothing but an illusion.  It is usually assumed, based on Plato's "Parmenides" (128a–d), that Zeno took on the project of creating these paradoxes because other philosophers had created paradoxes against Parmenides' view.  Thus Plato has Zeno say the purpose of the paradoxes "is to show that their hypothesis that existences are many, if properly followed up, leads to still more absurd results than the hypothesis that they are one."  ("Parmenides" 128d).  Plato has Socrates claim that Zeno and Parmenides were essentially arguing exactly the same point ("Parmenides" 128a–b). Atomism (from Greek ἄτομον , "atomon", i.e. "uncuttable", "indivisible") is a natural philosophy that developed in several ancient traditions.  The atomists theorized that nature consists of two fundamental principles: "atom" and "void".  Unlike their modern scientific namesake in atomic theory, philosophical atoms come in an infinite variety of shapes and sizes, each indestructible, immutable and surrounded by a void where they collide with the others or hook together forming a cluster.  Clusters of different shapes, arrangements, and positions give rise to the various macroscopic substances in the world. Buddhist atomism is a school of atomistic Buddhist philosophy that flourished on the Indian subcontinent during two major periods .  During the first phase, which began to develop prior to the 4th century BCE, Buddhist atomism had a very qualitative, Aristotelian-style atomic theory.  This form of atomism identifies four kinds of atoms, corresponding to the standard elements.  Each of these elements has a specific property, such as solidity or motion, and performs a specific function in mixtures, such as providing support or causing growth.  Like the Hindus and Jains, the Buddhists were able to integrate a theory of atomism with their logical presuppositions. Atomism or social atomism is a sociological theory arising from the scientific notion "atomic theory", coined by the ancient Greek philosopher Democritus and the Roman philosopher Lucretius.  In the scientific rendering of the word, atomism refers to the notion that all matter in the universe is composed of basic indivisible components, or atoms.  When placed into the field of sociology, atomism assigns the individual as the basic unit of analysis for all implications of social life.  This theory refers to "the tendecy for society to be made up of a collection of self-interested and largely self-sufficient individuals, operating as separate atoms".  Therefore, all social values, institutions, developments and procedures evolve entirely out of the interests and actions of the individuals who inhabit any particular society.  The individual is the ‘atom’ of society and therefore the only true object of concern and analysis. The unmoved mover (Ancient Greek: ὃ οὐ κινούμενον κινεῖ , "ho ou kinoúmenos kineî", "that which moves without being moved") or prime mover (Latin: "primum movens" ) is a concept advanced by Aristotle as a primary cause or "mover" of all the motion in the universe.  As is implicit in the name, the "unmoved mover" moves other things, but is not itself moved by any prior action.  In Book 12 (Greek "Λ") of his "Metaphysics", Aristotle describes the unmoved mover as being perfectly beautiful, indivisible, and contemplating only the perfect contemplation: itself contemplating.  He equates this concept also with the active intellect.  This Aristotelian concept had its roots in cosmological speculations of the earliest Greek Pre-Socratic philosophers and became highly influential and widely drawn upon in medieval philosophy and theology.  St. Thomas Aquinas, for example, elaborated on the unmoved mover in the "Quinque viae". The Pluralist school was a school of pre-Socratic philosophers who attempted to reconcile Parmenides' rejection of change with the apparently changing world of sense experience.  The school consisted of Anaxagoras, Archelaus, and Empedocles.  It can also be said to have included the Atomists, Leucippus and Democritus.  The Pluralists rejected the idea that the diversity of nature can be reduced to a single principle (monism).  Anaxagoras posited that nature contained an innumerable number of principles, while Empedocles reduced nature to four elements (fire, air, earth, and water) which could not be reduced to one another and which would be sufficient to explain change and diversity. Leucippus ( ; Greek: Λεύκιππος , "Leúkippos"; fl.  5th cent.  BCE) is reported in some ancient sources to have been a philosopher who was the earliest Greek to develop the theory of atomism—the idea that everything is composed entirely of various imperishable, indivisible elements called atoms. Leucippus often appears as the master to his pupil Democritus, a philosopher also touted as the originator of the atomic theory.  However, a brief notice in Diogenes Laertius’s life of Epicurus says that on the testimony of Epicurus, Leucippus never existed.  As the philosophical heir of Democritus, Epicurus's word has some weight, and indeed a controversy over this matter raged in German scholarship for many years at the close of the 19th century.  Furthermore, in his "Corpus Democriteum", Thrasyllus of Alexandria, an astrologer and writer living under the emperor Tiberius (14–37 CE), compiled a list of writings on atomism that he attributed to Democritus to the exclusion of Leucippus.  The present consensus among the world's historians of philosophy is that this Leucippus is historical.  The matter must remain moot unless more information is forthcoming from the record. Parmenides of Elea ( ; Greek: Παρμενίδης ὁ Ἐλεάτης ; fl.  late sixth or early fifth century BC) was a pre-Socratic Greek philosopher from Elea in Magna Graecia (Greater Greece, included Southern Italy).  He was the founder of the Eleatic school of philosophy.  The single known work of Parmenides is a poem, "On Nature", which has survived only in fragmentary form.  In this poem, Parmenides describes two views of reality.  In "the way of truth" (a part of the poem), he explains how reality (coined as "what-is") is one, change is impossible, and existence is timeless, uniform, necessary, and unchanging.  In "the way of opinion", he explains the world of appearances, in which one's sensory faculties lead to conceptions which are false and deceitful. The School of Abdera (or the Abderites) was a Pre-Socratic school of thought, founded in Abdera, Thrace around 440 to 430 BC.  Its proponents, Leucippus and Democritus, were the earliest atomists.  Leucippus is believed to be the founder, and was born at either Abdera or Miletus.  Democritus, his student, was native to Abdera.  Metrodorus of Chios and Anaxarchus of Abdera were also members, the latter being the teacher of Pyrrho who eventually came to lead the school and later founded Pyrrhonism.
Answer: Leucippus