Aper was the cognomen (or possibly the nickname) of a Roman general of the Third Century AD. His full name is thought to have been L. Flavius Aper. The information concerning him rehearsed here is derived from L.L. Howe’s history of the Praetorian Prefecture.
Aper is identified with the L. Flavius Aper who was the praepositus (commander) of a legionary detachment in Macedonia under Gallienus . Later he appears as a praeses (governor) of Pannonia. Under Numerian Aper was Praetorian Prefect, but he may have been appointed to that office earlier by Carus when Numerian was still Caesar.
As Praetorian Prefect he was able to contract a marriage between his daughter and the Caesar Numerian. He would also have been the (unnamed) Prefect who urged Carus to go to war with Persia. It was claimed that he did this in the hope that both Emperor and Caesar would perish in the course of the adventure thus opening his own way to the purple. Whether or not this assertion is well-founded is now unknowable. What is uncontestable is that when Numerian (by now the Emperor) died as the army returned from Persia Aper was accused of his murder by the army and put on trial. Diocles, commander of the Protectores Augusti Nostri, then gave early proof of the capacity for decisive action that was to distinguish him later as the Emperor Diocletian by pronouncing Aper the murderer and executing him on the spot with his own hands. It seems that the army considered that the charge supported by such conclusive proof of guilt was incontestable.