Lucius Flavius Aper was a Roman general who sought to become Emperor between August 277 and July 278.
Prior to his candidacy, he was stationed in Moesia Inferior, which was at that time administered by Faltonius Pinianus. He recognized Pinianus as Emperor in January 276, three months after Pinianus had declared himself Emperor. However, Aper became disillusioned with Pinianus after Pinianus failed to hold off a Gallo-Germanic invasion of Pannonia, and he declared himself Emperor on August 4, 277.
Aper was immediately recognized in Moesia Inferior, Thrace, and Bithnia and Pontus, and also by several generals stationed elsewhere. Shortly thereafter, Aper ordered forces loyal to him to march on Thessalonica, which Pinianus had made his provisional capital. Troops loyal to Pinianus were able to keep Aper's forces away from Thessalonica. After several months during which neither general made any significant gains over the other, a several units loyal to Pinianus sneaked into Bithnia and Pontus during May 278. Within forty days, they had reached Nicomedia, the province's capital; whereupon they arrested the governor who had defected to Aper and installed a new one loyal to Pinianus.
Aper had gained no new support after November 277. This was a result of a successful propaganda campaign by Pinianus blaming Aper for the losses in Pannonia. Even one general who had defected to Aper chose to defect back to Pinianus in January 278. Then after the fall of Nicomedia, many of the civil and military officers who had sided with Aper lost faith in him, and rejoined Pinianus' regime.
On July 8, 278, it was discovered that Aper had disappeared. His senior staff surrendered to Pinianus on July 18. Pinianus ordered a search for Aper to be undertaken soon after defeating the rebellion. By November, no evidence as to where Aper might have gone was found, so Pinianus ordered that the investigation be suspended indefinitely.