Apollonius the Grammarian was a Greek scholar who lived during the 2nd century CE, a period of the Roman Empire when the study of classical Greek language was highly developed. His precise life details, including his birthplace and education, are not recorded. He worked as a professional grammarian, part of a tradition producing technical handbooks on language, likely in major cultural centers like Alexandria or Rome.

He is credited with several prose works on specialized topics in grammar and vocabulary. One known treatise is On Similar and Different Words, which examines synonyms and fine distinctions in meaning. He is also associated with works on spelling (orthography) and possibly a word list (lexicon). The exact number and attribution of his writings are not fully certain, and some may be conflated with works by other grammarians named Apollonius.

According to modern scholars, Apollonius represents the specialized, technical study of Greek grammar that flourished during the era known as the Second Sophistic. His work contributed to the systematic analysis and preservation of classical Attic Greek, which was the standard for educated writing and speech. Grammarians like him created the foundational textbooks used in education, helping to transmit the rules and nuances of the Greek language to later generations, including scholars in the Byzantine period.