The anonymous Epitome de Caesaribus (25.1) introduces the emperor C. Julius Verus Maximinus (235–8 CE) for the first time as ‘Maximinus Thrax’. This is now a generally acceptable name for the emperor, despite the fact that it appears only once, here in the fourth century. So iconic is this geographical label, however, that the curious treatment of his origins by the most detailed sources, Herodian and the Historia Augusta, can be obscured. While both state that his birthplace was Thrace, they also point out that his origins were racially mixed. Herodian, a contemporary historian, calls Maximinus the son of mixobarbaroi, ‘mixed-barbarians’; a century and a half later, the Historia Augusta, in a long, largely fanciful biography, calls him a semibarbarus, a ‘half-barbarian’. His brief rule was therefore remembered as inaugurating a precedent that would come to plague the empire for decades: an emperor of dubious, even mongrel origins, elected by the troops, would bring cruelty and chaos to the state. This article considers how the Historia Augusta in particular used racial terms to highlight the difference between the legitimate rule of the senate and the illegitimate subversion of its authority by a half-barbarian from the periphery of the empire. This racial profile was fully formed only in the fourth century and is reflected in a range of other sources, demonstrating that contemporary political concerns brought to the fore debates on the dangers of racial mixing.