Marcus Aurelius Carinus, the elder son of Carus, was born around AD 250. He and his brother Numerian were elevated to the rank of Caesar (junior emperor) in AD 282.
When in December AD 282 or January AD 283 Carus left together with Numerian to campaign first on the Danube and then against the Persians, Carinus was left in Rome to direct the government of the west. It was for this purpose that Carinus was made consul as colleague to his father for 1 January AD 283.
It is fairly evident that Carinus was the prefered heir of Carus. He possessed that ruthlessness and military his brother Numerian did not have.
When Carus died later in AD 283, and Numerian took the position of Augustus in the east, there was no opposition and the rule of the joint emperors held the promise of being a reasonably peaceful reign.
Carinus' reputation as an emperor is among the worst of tyrants. He was a competent ruler and administrator of government, but so too he was a vicious personal tyrant. By marrying and divorcing he accumulated a list of nine wives, some of whom he divorced as they were pregnant. Further to this he appeared to have had a particular liking for affairs with wives of Roman noblemen.
Whilst Diocletian arose in the east, Carinus victoriously campaigned against Germans and the Britons (AD 284). But on hearing of Diocletian's revolt, he could not deal with him at once, as he had a second challenger to his power arise in Marcus Aurelius Julianus, the governor of Venetia, who revolted against him.
With this pretender out of the way Carinus could now deal with Diocletian. He moved up to the Danube where near Margum the two forces finally met.