Who appointed himself emperor of the western Roman Empire?

Self-appointed emperors in the west were: usurpers who were proclaimed by their legions and came into conflict with the actual emperor; Petronius Maximus after he was involved in the assassination of Valentinan III; Avitus, who was supported militarily by the Visigoths.

Odoacer did not proclaim himself emperor. After deposing Romulus Augustus he declared that Rome did not need an emperor, claimed that Romulus Augustus had given him governance of Italy and only asked for patrician status. Zeno, the emperor of the east, recognised Odoacer as governor of Italy on his behalf, provided that he recognised Julius Nepos (who had been deposed by Romulus Augustus' father) as emperor of the west. Jiulius Nepos was murdered by his own military leaders four years later.