Demetrius of Phaleron was an Athenian orator, statesman, and philosopher who lived from approximately 350 to 280 BCE, during the early Hellenistic period. He was a student of Theophrastus, which placed him within the Peripatetic school of philosophy founded by Aristotle. Following Athens's defeat by Macedon, Demetrius was appointed as governor of Athens from 317 to 307 BCE with Macedonian support. His rule is described as a moderate oligarchy that brought stability but reduced democratic freedoms. He was forced into exile when the city was captured by a rival Macedonian leader.

After his exile, Demetrius went to Alexandria in Egypt, where he served as an advisor to King Ptolemy I. According to ancient sources, he played a significant role in proposing the creation of the famous Library and Museum of Alexandria, though the precise extent of his involvement is debated by modern scholars. He later fell from favor and died in Egypt around 280 BCE.

Demetrius was a prolific writer, but none of his works survive in full. They are known only through fragments and references by later authors. His writings covered history, philosophy, and rhetoric. Notable lost works include On Fortune and On the Athenian Legislation. He is also credited with compiling the first written collection of Aesop's fables. A surviving rhetorical treatise called On Style was traditionally attributed to him, but scholars now believe it was written by a different, unknown author centuries later.

Demetrius is historically significant as a bridge between the Classical Greek world and the new Hellenistic kingdoms. His career exemplifies the philosopher-statesman ideal, and his move to Alexandria symbolizes the transfer of Greek intellectual culture to new centers of power. His alleged connection to the Library of Alexandria has made him a legendary figure in the story of ancient scholarship and the preservation of knowledge.