Divi filius is a Latin phrase meaning "son of a god", and was a title much used by the adopted son of Julius Caesar

Julius Caesar

Gaius Julius Caesar was a Roman general and statesman and a distinguished writer of Latin prose. He played a critical role in the gradual transformation of the Roman Republic into the Roman Empire....

, his great-nephew Octavian, the future Emperor Augustus

Augustus

Augustus ;23 September 63 BC – 19 August AD 14) is considered the first emperor of the Roman Empire, which he ruled alone from 27 BC until his death in 14 AD.The dates of his rule are contemporary dates; Augustus lived under two calendars, the Roman Republican until 45 BC, and the Julian...

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Octavian as son of a Roman god

On 1 January 42 BC, nearly two years after the assassination of Julius Caesar on 15 March 44 BC, but before the final victory

Liberators' civil war

The Liberators' civil war was started by the Second Triumvirate to avenge Julius Caesar's murder. The war was fought by the forces of Mark Antony and Octavian against the forces of Caesar's assassins Marcus Junius Brutus and Gaius Cassius Longinus in 42 BC.-Prelude:After the murder of Caesar,...

 of the Second Triumvirate

Second Triumvirate

The Second Triumvirate is the name historians give to the official political alliance of Octavius , Marcus Aemilius Lepidus, and Mark Antony, formed on 26 November 43 BC with the enactment of the Lex Titia, the adoption of which marked the end of the Roman Republic...

 over the conspirators who had taken his life, the Roman Senate

Roman Senate

The Senate of the Roman Republic was a political institution in the ancient Roman Republic, however, it was not an elected body, but one whose members were appointed by the consuls, and later by the censors. After a magistrate served his term in office, it usually was followed with automatic...

 recognised him as a divinity. He was therefore referred to as Divus Iulius (the divine Julius), and his adopted son styled himself Divi filius (son of the deified one, son of the god). The fuller form, "divi Iuli filius" (son of the divine Julius) was also used.

Octavian used the title divi filius to advance his political position, finally overcoming all rivals for power within the Roman state. The title was for him "a useful propaganda tool", and was displayed on the coins that he issued.

Other emperors

Since Augustus himself (the title "Augustus" was officially conferred on Octavian in 27 BC) and some other Roman Emperors were deified after death, the title Divi Filius was also applied to some of Augustus's successors: Tiberius

Tiberius

Tiberius , was Roman Emperor from 14 AD to 37 AD. Tiberius was by birth a Claudian, son of Tiberius Claudius Nero and Livia Drusilla. His mother divorced Nero and married Augustus in 39 BC, making him a step-son of Octavian...

, Nero

Nero

Nero , was Roman Emperor from 54 to 68, and the last in the Julio-Claudian dynasty. Nero was adopted by his great-uncle Claudius to become his heir and successor, and succeeded to the throne in 54 following Claudius' death....

, and Domitian

Domitian

Domitian was Roman Emperor from 81 to 96. Domitian was the third and last emperor of the Flavian dynasty.Domitian's youth and early career were largely spent in the shadow of his brother Titus, who gained military renown during the First Jewish-Roman War...

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Distinction from "Dei Filius"

The term used for Julius Caesar and the deified emperors was "divus", not "deus', the word used for gods such as Jupiter and Mars. Augustus was thus called "Divi Filius", not "Dei Filius", the phrase that Christians used of Jesus.