Gens Claudia was a notable patrician Roman house originating from the early Roman Republic. Members of this family frequently held political offices in the republic and later, the empire. The Claudian influence of the Julio-Claudian originates from the circumstances of the marriage of Livia Drusilla to Octavian, who would later become the first Roman Principate, Augustus.

Livia Drusilla was the daughter of Marcus Livius Drusus Claudianus (a member of gens Claudius) and his wife Aufidia. In 43 BCE she was married to her cousin Tiberius Claudius Nero, known as Tiberius Nero. It is interesting to note at this time that both her father and husband were allied with Cassius and Brutus against Octavian during the civil war that followed the assassination of Julius Caesar. Following their defeat at Phillipi, her father committed suicide while her husband joined Marcus and Lucius Antonius in the continued fight against Octavian. Livia and Tiberius Nero had a son they named Tiberius Claudius Nero in 42 BCE. The family was forced to flee Italy to Sicily and then to Greece in 40 BCE to avoid the proscriptions of the second triumvirate formed by Marcus Antonius (who had at this point briefly reconciled with Octavian), Marcus Aemilius Lepidus and Octavian. In 39 BCE a policy of amnesty allowed the family of Tiberius Nero to return to Rome.

Livia met Octavian for the first time that year while pregnant with her second child Nero Claudius Drusus who would be later known as Drusus the Elder. Octavian was himself married to Scribonia, daughter of Lucius Scribonius Libo the year before, from which they had one child, a daughter, Julia. Octavian divorced Scribonia the same day Julia was born while at the same time demanding Tiberius Nero divorce Livia to which he was either persuaded or forced to oblige. Drusus the Elder was born on the 14th of January, 38 BCE and Livia and Augustus were married three days later. This marriage continued on for 51 years until the death of Octavian (then referred to as Augustus) and never resulted in any children.

Tiberius married Julia in 11 BCE and was adopted by Augustus into gens Julia in AD 4, changing his name to Tiberius Julius Caesar. Tiberius ascended to the position of Princips following the death of Augustus in AD 14 thus establishing the Claudian influence within the Julio-Claudian dynasty. Tiberius' brother, Drusus the Elder's descendants would act as the subsequent three emperors of the Julio-Claudian dynasty as he was grandfather to Emperor Caligula (Gaius Julius Caesar Augustus Germanicus), father to the Emperor Claudius (Tiberius Claudius Caesar Augustus Germanicus) and great-grandfather to Emperor Nero (Nero Claudius Caesar Augustus Germanicus). It is worthy to note that Nero was not a member of the Claudii by birth as his ancestry was through his mother and the Romans observed patrilineal descent. Nero was born into the Domitii Ahenobarbi but became a Claudian in name when his mother Agrippina the Younger (granddaughter of Drusus the Elder) married her uncle Emperor Claudius. Nero's suicide in AD 68 brought the Julio-Claudian dynasty to a close which was eventually succeeded by the Flavian dynasty after a period of tumult referred to as the year of four emperors.

My sources are Tacitus' Annals and Suetonius' Lives of the Caesars.