Demonicus was a comic poet from ancient Athens who lived and worked during the Classical period, around the 5th to 4th centuries BCE. He is associated with the tradition of Old Comedy, the same style practiced by the famous playwright Aristophanes. No personal details about his life, background, or education have survived.

Ancient records credit him with writing two comedies: The Arrhephoroi and Philargyros. Both plays are now lost. The title The Arrhephoroi refers to the young girls who served in the Athenian cult of Athena, suggesting the play may have involved a mythological or religious theme. Philargyros translates to "Money-Lover," indicating a plot likely centered on the vice of greed. Only a single, brief fragment from The Arrhephoroi survives today.

According to modern scholars, Demonicus is considered a very minor figure. His primary significance lies in his inclusion in historical catalogs, which helps illustrate the wide range of comic production in ancient Athens beyond the handful of major playwrights whose works survive in full. The titles of his lost plays offer small clues about the variety of subjects explored in Old Comedy.