Gaius Julius Callistus (flourished 1st century) was a Greek imperial freedman during the reigns of Roman Emperors Caligula and Claudius. Callistus was originally a freedman of Caligula, and was given great authority during his reign, which he used to amass even greater wealth. He often advised Caligula on imperial policy and how to deal with emergent issues such as the abundant conspiracies against the emperor. He used his influence to help his friends, including Domitius Afer, whose treason case was dropped at Callistus' behest. However, Callistus was not immune from Caligula's wrath, and when a thwarted assassin named Callistus as a fellow conspirator in the failed plot, Caligula was ready to believe him. It was only pleading that saved Callistus' life.