Titus Flavius Josephus, born Yosef ben Matityahu, was a first-century Romano-Jewish historian who was born in Jerusalem—then part of Roman Judea—to a father of priestly descent and a mother who claimed royal ancestry.
He initially fought against the Romans during the First Jewish–Roman War as head of Jewish forces in Galilee, until surrendering in 67 CE to Roman forces led by Vespasian after the six-week siege of Jotapata. Josephus claimed the Jewish Messianic prophecies that initiated the First Jewish–Roman War made reference to Vespasian becoming Emperor of Rome. In response Vespasian decided to keep Josephus as a slave and presumably interpreter. After Vespasian became Emperor in 69 CE, he granted Josephus his freedom, at which time Josephus assumed the emperor's family name of Flavius.
Flavius Josephus fully defected to the Roman side and was granted Roman citizenship. He became an advisor and friend of Vespasian's son Titus, serving as his translator when Titus led the siege of Jerusalem in 70 CE. Since the siege proved ineffective at stopping the Jewish revolt, the city's pillaging and the looting and destruction of Herod's Temple soon followed.