Anicius Olybrius (died 2 November 472) was Roman emperor from July 472 until his death later that same year; his rule as augustus in the western Roman Empire was not recognised as legitimate by the ruling augustus in the eastern Roman Empire, Leo I (r. 457–474). He was in reality a puppet ruler raised to power by Ricimer, the magister militum of Germanic descent, and was mainly interested in religion, while the actual power was held by Ricimer and his nephew Gundobad.

Olybrius was born in Rome, in the ancient and powerful gens Anicia, of Italian descent.

According to the consensus of historians, he was related to the consul Anicius Hermogenianus Olybrius, whose wife and cousin, Anicia Juliana, had the same name that Olybrius gave to his own daughter. Other historians consider this questionable, as "Juliana" was a common name in the gens Anicia, and because Hermogenianus seems to have begotten only one daughter, who took chastity vows. Other possible fathers have therefore been proposed: either Anicius Probus (suggested by Settipani) or, according to some clues, Petronius Maximus.

Olybrius married Placidia, younger daughter of western augustus Valentinian III (r. 425–455) and his wife Licinia Eudoxia, thus creating a bond between a member of the senatorial aristocracy and the conjoined Valentinianic–Theodosian dynasties. The year of their wedding is not recorded, although the historian Priscus implies it took place before Gaiseric's Vandals sacked Rome (June 2–16, 455). Oost has pointed out that in his chronicle Hydatius wrote Placidia was unmarried as of 455.

Steven Muhlberger points out that many of the events in the chronicle of Hydatius are based on hearsay, that problems with his chronology "resulted from delays and distortions in the best information to which he had access," and thus the evidence from Hydatius is not as decisive as Oost believed. Regardless, the powerful magister militum Aetius had forced Valentinian to betroth Placidia to his own son Gaudentius, so Olybrius could not have married her before Aetius' death.

Emperor Valentinian killed Aetius on 21 September 454. The following year, Valentinian was killed by some soldiers who had served under Aetius, probably instigated by the patricius Petronius Maximus, who succeeded to the throne. Petronius, who was a high-ranking imperial officer and a member of a family belonging to the senatorial aristocracy, married the augusta Licinia Eudoxia, widow of Valentinian. He also elevated his own son Palladius to the rank of caesar and had him marry Eudocia, elder daughter of Valentinian.

According to those historians who believe that Olybrius was Petronius' son, it was in 455 that Olybrius married Placidia, between 17 April, when Petronius was acclaimed augustus, and 31 May, when he died; this would explain the marriage between Olybrius and Valentinian's younger daughter as a move to secure Petronius' legitimacy as emperor.

Another possibility is that Olybrius and Placidia were engaged in 455, and only after Gaiseric freed her from his possession in the early 460s were they at last married. Oost mentions this possibility in his book Galla Placidia Augusta. The surviving evidence is not sufficient to allow us to decide between these alternatives.