Marcus Clodius Pupienus Maximus was Roman emperor with Balbinus for 99 days in 238, during the Year of the Six Emperors. The sources for this period are scant, and thus knowledge of the emperor is limited. In most contemporary texts he is referred to by his cognomen "Maximus" rather than by his second nomen Pupienus.

The Roman emperor was the ruler and monarchical head of state of the Roman Empire, starting with the granting of the title augustus to Octavian in 27 BC. The term "emperor" is a modern convention, and did not exist as such during the Empire. Often when a given Roman is described as becoming emperor in English, it reflects his taking of the title augustus and later basileus. Another title used was imperator, originally a military honorific, and caesar, originally a surname. Early emperors also used the title princeps alongside other Republican titles, notably consul and pontifex maximus.