Gaius Caesar
Lacking any male child and heir, Augustus married his only child—a daughter -- Julia to his nephew Marcus Claudius Marcellus. Marcellus, however, died of food poisoning in 23 BC. Augustus then married his widowed daughter to his loyal friend, Marcus Vipsanius Agrippa, previously married to Augustus' niece, the sister of Marcellus. This marriage produced five children, three sons and two daughters: Gaius Caesar, Lucius Caesar, Julia the Younger, Agrippina the Elder, and Agrippa Postumus.