Constantine the Illyrian(?)
Constantine "the Great" is constantly called an Illyrian emperor in articles. Other posts try to refute this, mentioning he was not born in Illyricum, and born well after the Illyrians were overwhelmingly integrated into the Roman sphere. Some of these articles claim he was descended from an Italian family that colonized the Roman city. The man is directly or indirectly responsible for our current calendar, Sundays off, knees bent to Mary, and on and on. He's on par with or more impactful to European history than Genghis Khan, Charlemagne, he's Constantine after all. A number of people groups want to claim his legacy as part of their own, understandably so. He spoke Latin, his mother was Greek, his father a highly regarded military leader.
Just how “Illyrian” (or not) was the guy?
His descendants appear to have commissioned a fabricated genealogy well after his death, linking him with a few noteworthy Italian families, but this was most certainly done to justify their own right to rule in a manner more rational than “divine right” as was common, but evident to be little more than clout chasing.