Gellius Maximus (died 219) was a Roman usurper against Emperor Elagabalus. Gellius Maximus was the son of a physician and a member of the senate. He served as an officer in Legio IV Scythica in Syria and took advantage of the turmoil during the reign of Elagabalus to proclaim himself emperor. The rebellion was soon extinguished, and Gellius Maximus was executed.