Apotheosis means glorification, usually to a divine level, coming from the Greek word apotheoun, "to deify."

Apotheosis is most commonly used to refer to the Roman pagan process whereby an Emperor was made into or recognized as a deity. Some Roman emperors underwent apotheosis upon their deaths. The process involved the creation of a waxen image of the emperor sitting in state, adorned with rich raiments and jewelry for a period of days, after which it would be burnt.

The apotheosis of an Emperor was an essentially political act performed by the dead emperor's successor. The tradition began with the declaration by the Senate of Julius Caesar's deification after his assassination in 44 BC, an act that shocked the urbane opinion of the Roman elite. When Augustus died 58 years later, he received similar honors, thus setting the pattern for future emperors. The aims of the act were to reinforce the majesty of the imperial office, and, more immediately, to associate the current emperor with a well-regarded predecessor. For instance, when Septimius Severus overthrew Didius Julianus to gain power in AD 193, he arranged the apotheosis of Pertinax, who had ruled before Julianus. This allowed Severus to present himself as the heir and successor to Pertinax, though the two were not related.

Apotheosis was not an automatic process, at least in the early empire. Emperors who were not fondly remembered, or who were disliked by their succesors, were generally not deified. For instance, Caligula and Nero, who were both regarded by many contemporaries as tyrants and whose reigns ended violently, were not regarded as gods after their deaths.

Emperors who had been deified were referred to with the word 'divus' before their names. Thus, Claudius was called 'divus Claudius.' This word is often rendered as 'god' (i.e., "Claudius the god") but that is something of an overtranslation; a better translation might be 'divine' (i.e., "the divine Claudius"), a somewhat softer formulation that Roman intellectuals could comfortably understand as metaphorical. In the later empire, this honor became more and more automatically associated with dead emperors, to the extent that it might just as well be understood as meaning 'late' (i.e., "the late Claudius"). The fact that 'divus' had lost much of whatever truly religious meaning it had is made clear by the fact that it was used with names of early Christian emperors after their deaths (e.g., "divus Constantinus").

As apotheosis became a part of Roman political life in the late Republic and early Empire, it began to be treated in literary contexts: In the Aeneid, Vergil depicts Aeneas' deification, saying he will be taken up to the stars of Heaven, and mentions Caesar's apotheosis. Publius Ovidius Naso also describes Caesar's apotheosis in book XV of The Metamorphoses and looks forward to the glorification of Octavius.

The notion of apotheosis was parodied by Lucius Annaeus Seneca in his Apocolocyntosis divi Claudii (The Pumpkinification of the Emperor Claudius), in which Claudius is transformed, not into a god, but into a pumpkin. This satirical work not only pokes fun at the notion that the notoriously clumsy and ill-spoken Claudius might be a deity, but also reveals a certain irreverance towards the idea of ruler cult, at least among Rome's educated classes.

Later artists have used the concept for motives ranging from real respect for the deceased (Constantino Brumidi's fresco "The Apotheosis of George Washington" on the dome of the United States Capitol Building in Washington, D.C.), to artistic comment (Salvador Dalí's Apotheosis of Homer), to comedic effect.