Callisthenes of Olynthus was a Greek historian of the 4th century BCE. A relative and student of the philosopher Aristotle, he originated from the city of Olynthus in northern Greece. He is best known for serving as the official historian on the military campaign of Alexander the Great, accompanying him to record his deeds and the geography of the lands they traversed.

His relationship with Alexander eventually deteriorated. Callisthenes was noted for his outspoken adherence to traditional Greek customs, and he publicly refused to perform the Persian ritual of bowing before the king. He fell from favor and was later implicated in a conspiracy against Alexander. The precise circumstances of his fate are uncertain; ancient sources report he was either executed, died in prison, or was crucified.

None of Callisthenes' own writings survive intact, but they are known through fragments quoted by later authors. His major works included a history of Greece and an official ten-book history of Alexander's campaign. This work initially portrayed Alexander in a heroic and divine light. After their fallout, however, Callisthenes' history also became a source for more critical accounts of Alexander's reign. Modern scholars consider his lost work a crucial primary source for the later historical tradition about Alexander.

Callisthenes' legacy is twofold. He remains a significant, tragic figure in classical historiography. Centuries after his death, a fictionalized account of Alexander's life was falsely attributed to him. This forged text, known as Pseudo-Callisthenes, became the foundation for many legendary medieval stories about Alexander.