Iulus is the semi-divine ancestor of ￼gens￼ Iulia, a patrician family at Rome. Legends vary. Iulus was identical with Ascanius, King of Alba Longa (Vergil), or he was a half-brother of Ascanius and son of Aeneas by his Trojan wife, Creüsa (Livy), or he was son of Ascanius (Dionysius of Halicarnassus, ￼Roman Antiquities￼ 1.70). It is not known which version was accepted by the Iulii themselves.
The Iulii were undoubtedly of Alban origin. They were mentioned as one of the leading Alban families removed to Rome and enrolled among the ￼patres￼ there by Tullus Hostilius after the destruction of Alba Longa. (Dionys. 3.29; Tac. Ann. 11.24; in Liv. 1.30 the reading should probably be Tuttios, not Julios.)
Nevertheless, the Iulii were mentioned in Roman legend even before the destruction of Alba Longa. Proculus Julius is said to have announced the passing of Romulus to the Roman people. He had a vision of Romulus, who bid the Roman people to worship him thereafter as the god Quirinus.