Bion of Borysthenes was a Hellenistic philosopher of the 3rd century BCE. He was born in the Greek colony of Olbia on the Black Sea. Ancient accounts describe a difficult early life: his father was a freedman and his mother a prostitute, and Bion was sold into slavery as a youth. He was later purchased and freed by a rhetorician, whose inheritance allowed Bion to travel to Athens to study philosophy.

In Athens, he studied under several schools but ultimately became a follower of the Cynics, particularly Crates of Thebes. He later served as a philosophical advisor at the Macedonian court of King Antigonus II Gonatas. He died in Chalcis.

Bion wrote no surviving complete works. He was famous for his "diatribes"—popular, satirical moral lectures that blended serious ethics with humor and streetwise rhetoric. These works survive only in fragments and paraphrases quoted by later authors.

According to modern scholars, Bion is significant for popularizing Cynic and Stoic ideas. His innovative, accessible style is seen as a key influence on later Hellenistic philosophers and the Roman poet Horace. His life story was often cited in antiquity as an example of philosophy's power to overcome humble origins.