Flavius Claudius Julianus (Julian) was born in Constantinople in 332 AD. His mother, Basilina, died a few months later. Julian's father, Julius Constantius, was the half-brother of the Emperor Constantine. When Julian was 5, Constantine died, and his sons Constantine II, Constantius II, and Constans took power. The co-emperors arranged for the murder of Julius Constantius and other family members as potential rivals. Julian and his half-brother Gallus were among the few survivors.

Julian went to exile in Nicomedia, where Mardonius served as his tutor and surrogate parent. In 342, Julian was sent to an isolated castle called Macellum, under the care of George, bishop of Casesarea. He was taught Christianity in both locations, though he was more excited about Homer and Hellenic philosophy. He continued his studies in Constantinople, Bithynia, and Athens. Julian learned Neoplatonism from the leading philosophers of the day and was initiated into the Mithras mystery religion.

In 355, Constantius made Julian a Caesar and had him marry Constantius's sister Helena. Constantius sent Julian to Gaul to fight the Alamanni and Frank tribes. Despite his initial figurehead status and a lack of military experience, Julian managed to gain control of the Roman army and defeat the German barbarians. He earned the support of the Roman army and, after ruling the area justly, the local population.

Constantius, viewing Julian as a rival, ordered him to transfer half of his army assist the campaign in Persia. Many of the troops, from Gaul, chose not to leave. Instead, they mutinied and proclaimed Julian their emperor. Julian reluctantly accepted the title. Constantius and Julian tried, without success, to negotiate a peaceful settlement. In 361, they led their armies towards one another in a potential civil war. Constantius died before the armies met, and Julian become the sole emperor of Rome.

As Emperor, Julian is best known for his support of paganism and opposition to Christianity. He halted imperial support of churches. Instead, he restored pagan temples and assisted pagan clergy. He forbid Christians from teaching the classics. He wasn't able to stop the long-range growth of Christianity, though later generations called him Julian the Apostate. He died in 363 while fighting the Persians, though it is unclear whether a Persian or a Roman Christian killed him.