In Greek and Roman mythology, Ascanius was a son of Aeneas and Creusa. After the Trojan War, Aeneas escaped to Latium in Italy with his father and fought in the Italian Wars. Virgil's Aeneid says he had a role in the founding of Rome as the first king of Alba Longa.
He was also called Iulus or Julus. From this name comes the Gens Julia, the Julian family to which Julius Caesar belonged.
The name Iulus was popularised by Virgil in his work the Aeneid, replacing the Greek name Ascanius by Iulus to try and link the Julian family of Rome to previous mythology. The emperor Augustus, who commissioned the work, was a member of the Julian family, so by spreading around, through his many poets (he was thought of as a great patron of the arts), his direct descent from Aeneas, he could claim to have three major Olympian gods in his family tree.