Seleucus was a general under Alexander the Great and later became the founder of the Seleucid Empire after Alexander's death in 323 BCE. He established his rule over a vast territory that included parts of modern-day Turkey, Syria, Iraq, and Iran. Seleucus is known for his efforts to spread Greek culture and influence throughout his empire. He faced numerous challenges, including conflicts with other successors of Alexander, known as the Diadochi. Seleucus successfully expanded his empire and established several cities, including Antioch, which became a major center of Hellenistic culture. His reign lasted until his assassination in 281 BCE.