Aper

…adoptive father, the praetorian prefect Aper, was accused of having killed him in order to seize power. When Diocletian, acclaimed as emperor by his soldiers, appeared for the first time in public dressed in the imperial purple, he declared himself innocent of Numerian’s murder. He designated Aper as the criminal…

His father-in-law, Aper, who had assumed command, was accused of his murder and executed, and the throne passed to Diocletian, commander of the household guards.