Aetius was a compiler of philosophical knowledge who lived during the Roman period, likely in the 1st or 2nd century CE. No details of his personal life are known; his existence and name are a modern reconstruction by scholars. His role was that of a doxographer, meaning he specialized in collecting and organizing the stated opinions of earlier Greek philosophers.

His sole known work is the Placita Philosophorum (The Opinions of the Philosophers). This was a comprehensive handbook that systematically listed the doctrines of major schools—including Presocratic, Platonic, Aristotelian, Stoic, and Epicurean thinkers—under thematic topics like the principles of the universe or the nature of the soul. The original text is lost, but its contents are preserved through later works that used it as a source. Modern scholars have reconstructed Aetius's compilation from these later writings.

Aetius's historical importance is as a preserver and systematizer. His work represents the peak of a long tradition of doxography, creating a structured reference manual that was widely used by later writers, educators, and encyclopedists in antiquity and the Byzantine era. For modern study, his reconstructed text is an indispensable secondary source for the theories of many early Greek philosophers whose original works have been lost, providing a crucial window into how philosophical knowledge was categorized and transmitted in the early Roman Empire.