Question: Who thought atoms and the void comprised all of reality?

Disambiguated questions and answers:
context: No context provided
question: Who originally thought atoms and the void comprised all of reality?
short_answers: Democritus

context: Epicurus (341–270 BCE) studied atomism with Nausiphanes who had been a student of Democritus. Although Epicurus was certain of the existence of atoms and the void, he was less sure we could adequately explain specific natural phenomena such as earthquakes, lightning, comets, or the phases of the Moon (Lloyd 1973, 25–6). Few of Epicurus' writings survive and those that do reflect his interest in applying Democritus' theories to assist people in taking responsibility for themselves and for their own happiness—since he held there are no gods around that can help them. He understood gods' role as moral ideals.
question: Who, as a student of Democritus, thought atoms and the void comprised all of reality?
short_answers: Epicurus
wikipage: Atomism

context: No context provided
question: Who is the mentor thought atoms and the void comprised all of reality?
short_answers: Leucippus

context: In the 5th century BCE, Leucippus and his pupil Democritus proposed that all matter was composed of small indivisible particles called atoms. Nothing whatsoever is known about Leucippus except that he was the teacher of Democritus. Democritus, by contrast, was a prolific writer, who wrote over eighty known treatises, none of which have survived to the present day complete. However, a massive number of fragments and quotations of his writings have survived. These are the main source of information on his teachings about atoms. Democritus's argument for the existence of atoms hinged on the idea that it is impossible to keep dividing matter for infinity and that matter must therefore be made up of extremely tiny particles.
question: Who is the pupil thought atoms and the void comprised all of reality?
short_answers: Democritus
wikipage: Atomism

Long answers:
knowledge: content: In the 5th century BCE, Leucippus and his pupil Democritus proposed that all matter was composed of small indivisible particles called atoms.
wikipage: Atomism

content: Democritus (/dɪˈmɒkrɪtəs/; Greek: Δημόκριτος, Dēmókritos, meaning "chosen of the people"; c. 460 – c. 370 BC) was an Ancient Greek pre-Socratic philosopher primarily remembered today for his formulation of an atomic theory of the universe.[3]
wikipage: Democritus

content: Leucippus, the founder of atomism, was the greatest influence upon him.
wikipage: Democritus

content: Leucippus (/luːˈsɪpəs/; Greek: Λεύκιππος, Leúkippos; fl. 5th century 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.
wikipage: Leucippus

content: Democritus, along with Leucippus and Epicurus, proposed the earliest views on the shapes and connectivity of atoms.
wikipage: Democritus

content: Epicurus[a] (341–270 BC) was an ancient Greek philosopher and sage who founded Epicureanism, a highly influential school of philosophy. He was born on the Greek island of Samos to Athenian parents. Influenced by Democritus, Aristippus, Pyrrho,[3] and possibly the Cynics, he turned against the Platonism of his day and established his own school, known as "the Garden", in Athens. 
wikipage: Epicurus
long_answer: The ancient Greek philosopher, Leucippus, is thought to have developed the theory of atomism—the idea that everything is composed entirely of various imperishable, indivisible elements called atoms. Democritus studied under Leucippus and is well known for his formulation of an atomic theory. Another philosopher of the time, was Epicurus. He was greatly influenced by Democritus. Together, the three proposed the earliest views on the shapes and connectivity of atoms.

knowledge: content: Democritus (/dɪˈmɒkrɪtəs/; Greek: Δημόκριτος, Dēmókritos, meaning "chosen of the people"; c. 460 – c. 370 BC) was an Ancient Greek pre-Socratic philosopher primarily remembered today for his formulation of an atomic theory of the universe.
wikipage: Democritus

content: Leucippus (/luːˈsɪpəs/; Greek: Λεύκιππος, Leúkippos; fl. 5th century 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.
wikipage: Leucippus

content: Epicurus[a] (341–270 BC) was an ancient Greek philosopher and sage who founded Epicureanism, a highly influential school of philosophy.
wikipage: Epicurus
long_answer: Several philosophers thought atoms and the void comprised all of reality. The Ancient Greek pre-Socratic philosopher Democritus, a pupil of Leucippus, originally did. In the 5th century BCE, Democritus and his mentor, Leucippus, proposed that all matter was composed of small indivisible particles called atoms. As a student of Democritus, the ancient Greek philosopher Epicurus also believed atoms and the void comprised all of reality.