Theagenes of Macedon was a Hellenistic historian of the 3rd century BCE. No biographical details survive beyond his Macedonian origin and his role as a historian writing in the Koine Greek dialect. His only known work is a history of Alexander the Great.

This text is now lost, preserved only in fragments cited by later authors such as Aelian in his Varia Historia. Theagenes is a minor, fragmentary source within the Alexander historiographical tradition. The surviving citation, which references Alexander’s consultation of the oracle of Ammon, suggests his work included anecdotal material. His significance lies primarily as one of the many lost sources that informed later historical accounts.