Aristotle (Ancient Greek: Ἀριστοτέλης, Aristotélēs) (384 BC – 322 BC) was a Greek philosopher and polymath, a student of Plato and teacher of Alexander the Great. His writings cover many subjects, including physics, metaphysics, poetry, theater, music, logic, rhetoric, linguistics, politics, government, ethics, biology, and zoology. Together with Plato and Socrates (Plato's teacher), Aristotle is one of the most important founding figures in Western philosophy. Aristotle's writings were the first to create a comprehensive system of Western philosophy, encompassing morality, aesthetics, logic, science, politics, and metaphysics.

Aristotle's views on the physical sciences profoundly shaped medieval scholarship, and their influence extended well into the Renaissance, although they were ultimately replaced by Newtonian physics. In the zoological sciences, some of his observations were confirmed to be accurate only in the 19th century. His works contain the earliest known formal study of logic, which was incorporated in the late 19th century into modern formal logic. In metaphysics, Aristotelianism had a profound influence on philosophical and theological thinking in the Islamic and Jewish traditions in the Middle Ages, and it continues to influence Christian theology, especially the scholastic tradition of the Catholic Church. His ethics, though always influential, gained renewed interest with the modern advent of virtue ethics. All aspects of Aristotle's philosophy continue to be the object of active academic study today. Though Aristotle wrote many elegant treatises and dialogues (Cicero described his literary style as "a river of gold"), it is thought that the majority of his writings are now lost and only about one-third of the original works have survived.

Ivan IV Vasilyevich (Russian:  Ива́н Четвёртый, Васи́льевич​ (help·info), Ivan Chetvyorty, Vasilyevich; 25 August 1530 – 28 March [O.S. 18 March] 1584), known in English as Ivan the Terrible (Russian:  Ива́н Гро́зный​ (help·info), Ivan Grozny; lit. Fearsome), was Grand Prince of Moscow from 1533 until his death. His long reign saw the conquest of the Khanates of Kazan, Astrakhan, and Siberia, transforming Russia into a multiethnic and multiconfessional state spanning almost one billion acres, approximately 4,046,856 km² (1,562,500 sq mi). Ivan managed countless changes in the progression from a medieval state to an empire and emerging regional power, and became the first ruler to be crowned as Tsar of all Russia.

Historic sources present disparate accounts of Ivan's complex personality: he was described as intelligent and devout, yet given to rages and prone to episodic outbreaks of mental illness. On one such outburst Tsar beat and unpremeditatedly killed his groomed and chosen heir Ivan Ivanovich. This led Tsardom to be passed to Tsar's younger son: the weak and intellectually disabledFeodor I of Russia. Ivan's legacy is complex: he was an able diplomat, a patron of arts and trade, founder of the Russia's first Print Yard, but he is also remembered for his paranoiac suspiciousness and cruel persecution of nobility.