Ricimer (/ˈrɪsɪmər/ RISS-im-ər, Latin: [ˈrɪkɪmɛr]; c. 418 – 19 August 472) was a Romanized Germanic general, who ruled the remaining territory of the Western Roman Empire from 456 after defeating Avitus, until his death in 472, with a brief interlude in which he contested power with Procopius Anthemius. Deriving his power from his position as magister militum of the Western Empire, Ricimer exercised political control through a series of puppet emperors. Ricimer's death led to unrest across Italy and the establishment of a Germanic kingdom on the Italian Peninsula.

The date of Ricimer's birth is unknown. Some scholars have dated it as late as the early 430s, which would have made him unusually young when he rose to power. A birthdate of around 418 is more likely. The names of his parents are also unknown. In his panegyric to Anthemius, given in 468, the poet Sidonius Apollinaris claimed that Ricimer was Suevic on his father's side and Visigothic on his mother's, specifying that his maternal grandfather was Wallia, King of the Visigoths, who died in 418. It has been suggested that his Suevic father may have been a son of Hermeric, the king of the Suevi around 418, or else possibly Hermegarius, a Suevic war leader who died in 429.

It has been surmised that Ricimer was the offspring of a marriage alliance between the ruling Suevic and Gothic houses and although Ricimer's father was identified as a Sueve, his identity is more frequently attested as Gothic by ancient writers. Such an alliance has been suggested as occurring in the year 431, but a more likely date is anterior to Wallia's death in 418. Wallia's Visigothic successors were not his close relatives and may have been hostile toward the family members of the former king.

As entry into the Western Empire's military was a frequent option for "losers of struggles for leadership among the barbarians", Ricimer's family may have entered the service of Rome. Historian Peter Heather suggests that the lack of stability among the Visigoths themselves may have incentivized Ricimer's pursuit of an "entirely Roman career", despite being "the grandson of the Visigothic king Wallia".

Like many Germanic figures of note, Ricimer had relational ties to other tribes, like the Burgundians. For instance, Gundobad, Ricimer's "subordinate and successor", was his nephew since his sister had married the Burgundian king Gondioc.

According to Sidonius Apollinaris, Ricimer served under the magister militum Aetius alongside the comes domesticorum Majorian, whom he befriended. Historian Penny MacGeorge writes, "Majorian certainly, and Ricimer probably, had served under Aetius, and there may have been other elements to this connection, political, personal, and social, that would have brought them both close to the centers of political power."

Nonetheless, a power vacuum was created in the Western Empire after the events of 454 and 455, which saw the consecutive murders of Aetius and of the Western Emperor Valentinian III, who had been responsible for the magister militum's assassination. After the assassinations, the Roman Senator Petronius Maximus proclaimed himself emperor. Petronius's reign lasted less than three months, as shortly before the Vandal sacking of Rome in 455, he too was murdered.

After Rome's sack, the Visigothic King Theodoric II proclaimed Avitus as Emperor, the Roman military commander in Gaul. In return for Theodoric II's support, Avitus agreed to allow the Visigoths to enter Suevi-controlled Hispania. After being proclaimed the new emperor in 456, Avitus mounted a campaign into Italy but was defeated in the Po Valley. In the interim, Avitus had named the Visigoth Remistus as magister militum.