Aelius Theon was a Greek teacher of rhetoric, or a sophist, who was active in the city of Alexandria during the 1st century CE, a period when Egypt was part of the Roman Empire. The precise dates of his life are uncertain, but he is generally thought to have been teaching around the middle of that century. According to later historical sources, he was known as a skilled orator and was the teacher of other notable scholars.

His primary importance lies in a single surviving textbook he wrote, called the Progymnasmata, which means "preliminary exercises." This work is the oldest complete manual of its kind that has survived from antiquity. It outlines a structured series of practice exercises for students learning public speaking and composition. The lessons start with simple tasks, like retelling a fable or a historical narrative, and gradually advance to more complex challenges, such as arguing for or against a proposed law or writing a speech that praises or blames a person.

Modern scholars view Theon's Progymnasmata as a crucial source for understanding ancient education. It provides a clear window into the teaching methods used by rhetoricians in the early Roman Empire and shows how students were trained in the skills of Greek rhetoric. This textbook served as a foundation for later, more famous rhetoric manuals and influenced educational practices for centuries.