Marcus Claudius Marcellus (42-23 BC) was the eldest son of Octavia Minor, sister of Augustus, and Gaius Claudius Marcellus Minor, a former consul. He was descended through his father from Marcus Claudius Marcellus, a famous general in the Second Punic War.
Velleius, a pro-Augustan source, states that:
People thought that, if anything should happen to Caesar, Marcellus would be his successor in power, at the same time believing, however, that this would not fall to his lot without opposition from Marcus Agrippa. He was, we are told, a young man of noble qualities, cheerful in mind and disposition, and equal to the station for which he was being reared.
This passage supports the suggestion in Tacitus and other historians that other potential heirs such as Tiberius and Agrippa felt threatened by Marcellus's rise. After the marriage Agrippa set out for Asia "on the pretext of commissions from the emperor, but, according to current gossip, was in fact withdrawing for the time being, on account of his secret animosity for Marcellus". In addition, Dio states that:
[Augustus] well understood that Agrippa was exceedingly beloved by the people and he preferred not to seem to be committing the supreme power to him on his own responsibility. When he recovered, for, and learned that Marcellus because of this was not friendly toward Agrippa, he immediately sent the latter to Syria, so that no occasion for scoffing or for skirmishing might arise between them by their being together. And Agrippa straightway set out from the city, but did not reach Syria; instead, acting with even more than his usual moderation, he sent his lieutenants thither, and tarried himself in Lesbos.
Augustus gave him a public burial after the customary eulogies, placing him in the tomb he was building ... And he ordered also that a golden image of the deceased, a golden crown, and a curule chair should be carried into the theatre [of Marcellus] at the Ludi Romani and should be placed in the midst of the officials having charge of the games.
This he did later; at the time, after being restored to health, he brought his will into the senate and desired to read it, by way of showing people that he had left no successor to his realm; but he did not read it, for none would permit it. Absolutely everybody, however, was astonished at him because, although he loved Marcellus both as son-in‑law and nephew.... nevertheless he had not entrusted to him the monarchy, but actually had preferred Agrippa before him. Thus it would appear that he was not yet confident of the youth's judgment, and that he either wished the people to regain their liberty or for Agrippa to receive the leadership from them.
Augustus also had funerary statues of Marcellus set up, such as the Marcellus as Hermes Logios.
Agrippa swiftly returned from Asia after Marcellus's death, and Marcellus's widow Julia was soon married to him. Marcellus was added by Virgil at the end of the list of illustrious future Romans whom Aeneas sees in the underworld in Book VI of the Aeneid. This passage - recounting Marcellus's life, connecting him to his illustrious ancestor Marcellus the Elder, and lamenting his tragically early death - is said to have caused Octavia to faint with grief when it was read to her and Augustus.