Gallienus

Born around 218 to a senatorial family, Gallienus became co-emperor with his father Valerian in 253, taking command of the western half of the empire while Valerian ruled the east. He put down the usurper Ingenuus in 258 and shattered an Alemanni invasion at Mediolanum the following year. When Valerian was captured by the Sasanian Empire at Edessa in 260, the empire fractured into civil war and full control passed to Gallienus. He crushed eastern usurpers Macrianus Major and Lucius Mussius Aemilianus in 261-262, but couldn't prevent general Postumus from carving out the breakaway Gallic Empire. In 268, facing another rival - Aureolus, who'd proclaimed himself emperor in Mediolanum - Gallienus defeated him outside the city and began a siege. During that siege, in September 268, the officer Cecropius stabbed him to death as part of a conspiracy.