Petronius Maximus (c. 397 – 31 May 455) was Roman emperor of the West for two and a half months in 455. A wealthy senator and a prominent aristocrat, he was instrumental in the murders of the Western Roman magister militum, Aëtius, and the Western Roman emperor, Valentinian III.

Maximus secured the throne the day after Valentinian's death by ensuring the backing of the senate and by bribing the palace officials. He strengthened his position by forcing Valentinian's widow to marry him and forcing Valentinian's daughter to marry his son. He cancelled the betrothal of his new wife's daughter to the son of the Vandal king Genseric. This infuriated both his stepdaughter and Genseric, who sent a fleet to Rome. Maximus failed to obtain troops from the Visigoths and he fled as the Vandals arrived, became detached from his retinue and bodyguard in the confusion, and was killed. The Vandals thoroughly sacked Rome.