Arius Didymus was a Stoic philosopher from Alexandria who lived and worked in the 1st century BCE. He is historically significant for his close association with the first Roman emperor, Augustus. According to ancient sources, Augustus was so impressed by Arius during a visit to Alexandria that he invited the philosopher to Rome. Arius is said to have served as a court advisor and even consoled the emperor after the death of a close friend, illustrating the integration of Greek philosophers into early imperial Roman circles.

While no complete works by Arius survive, his writings are known through quotations by later authors, especially the 5th-century anthologist Stobaeus. He is credited with composing detailed summaries, or epitomes, of philosophical doctrines. The two major works attributed to him are an Epitome of Stoic Ethics and an Epitome of Peripatetic Ethics. Some scholars believe he also wrote summaries covering physics and other schools of thought, though the exact scope of his authorship is debated.

Arius Didymus holds great importance as a source for understanding Hellenistic philosophy. His compiled summaries provide extensive accounts of Stoic and Aristotelian ethical teachings, which are crucial for reconstructing the philosophical debates of his era. According to modern scholars, his work represents a key phase in the history of philosophy, where thinkers aimed to systematically preserve and explain earlier ideas for educational purposes. His role also symbolizes the patronage of Greek learning by Roman power, helping to transmit philosophical ideas into Roman elite culture.