Apollonius Dyscolus was a Greek scholar who lived and worked in Alexandria, Egypt, during the 2nd century CE, a period when the region was part of the Roman Empire. He was a grammarian, meaning he specialized in the systematic study of language. His nickname "Dyscolus," which means "the Surly" or "the Difficult," likely referred to his challenging personality or the complex nature of his work. He was part of a family of scholars; his father was also a grammarian, and his son, Aelius Herodianus, became a prominent grammarian as well. According to later accounts, Apollonius was blind in his later life.

Apollonius wrote many technical treatises on different parts of Greek grammar. His most important and complete surviving work is On Syntax, which is in four books. Other surviving treatises include On Pronouns, On Conjunctions, and On Adverbs. Many of his other works are lost or survive only in fragments.

Modern scholars consider Apollonius Dyscolus a foundational figure in the history of linguistics. His major work, On Syntax, represents the first known systematic and theoretical analysis of how sentences are structured in any language. He established a framework for understanding the relationships between words and the functions of different parts of speech. His rational, principle-based approach influenced later Greek, Roman, and Byzantine grammarians. His theories were a major source for the influential Latin grammarian Priscian in the 6th century CE, thereby helping to shape the study of grammar in medieval Europe.