Arrius Aper

Arrius Aper was the praetorian prefect, and the father-in-law of the emperor Numerian. He murdered the emperor, as it was said, on the retreat of the army from Persia to the Hellespont. He carefully concealed the death of Numerian, and issued all the orders in his name, until the soldiers learned the truth by breaking into the imperial tent on the Hellespont. They then elected Diocletian as his successor, in the year 284, who straightway put Aper to death with his own hand without any trial.

Flavius Vopiscus relates that Diocletian did this to fulfill a prophecy which had been delivered to him by a female druid, "Imperator eris, cum Aprum occideris."