Probably the most infamous roman emperor of late antiquity is Phocas, a former centurion of the Balkan army, crowned emperor in 602.

Modern literature almost unanimously paints him as a cruel tyrant who not only slew his predecessor Maurice but also oppressed his people. >>

However, engaging closely with both primary sources and structural characteristics of late Roman monarchy, it turns out that the picture of Phocas as a tyrant is due to be critically revised.

This has lately been pointed out by Meier, Phokas als Erinnerungsproblem, 2014. >>

Following riots that resulted in Maurice’s overthrow, Phocas was publicly acclaimed and recognised as legitimate emperor.

Yes, sources record various clashes between him and his people in the following years; but those riots are quite common in late antique Constantinople. >>

From 602 to 610, Phocas was emperor.

The label tyrant is mainly a retrospect one; a tyrant is a failed emperor.

Phocas turned from emperor into tyrant only the moment he was overthrown by Heraclius in October 610. >>

Heraclius – who was just as much an emperor as Phocas had been, acclaimed by people and elites of Constple, crowned by the patriarch – instantly started to build his own, positive image.

… and what better way is there than distancing yourself from your murdered predecessor? >>

By vilifying Phocas as tyrant, by creating a negative foil, Heraclius could emerge as god-chosen emperor. This smear campaign can be traced through various sources, all originating after Heraclius’ accession. >>

Heraclius' smear campaign against Phocas turned out to be an extremely successful pr strategy, classic damnatio memoriae.
... successful to the extent that even some modern scholars keep falling for it.