Was reading a book from 1950 by A. A. Vasiliev on Justin I who, while he didn't explicitly make the claim, seemed to tacitly agree with other historians in this time period that the Slavs were already in the Balkan region before the 6th century, and that specifically Justinian, if not actually slavic, had slavic ancestry (p.50 for reference).
Now, I'm used to thinking the Slavs didn't appear in the record until the mid 6th century and they were still on the other side of the Danube then, with them not moving into the Balkans until the late 6th century along with the Avars. I'm pretty sure this is still the case with western historiography, but I'm curious if eastern european or russian historiography still differs, considering that it would serve slavic nationalistic purposes for Justinian to be of Slav descent.
I'm very mindful too, that this could be the perspective Vasiliev is writing from, considering 1950 is not too far from the "race-obsessed" nationalism of pre to WW2 period, and that even if this belief is debunked amongst slavic scholars, I'm curious if it is still retained amongst popular sentiment.
Do you speak any Russian? Here you can have a collection of sources which according to the Russians scholars in any way pertain to the ancient slavs.
IIRC it's not just the slavs who are identified with the slavs but also the Antes and the Venetoi. The latter got the honor since in all of the Germanic languages along with Finnish it is the traditional word for the Slavs. And in Byzantium one of the Hippodrome parties were the Venetoi (the blues) which I guess was important for Slavophiles.
Slavophilia in Russia was revived in Russia mainly in the Stalin era, amongst other things because Hitler picked up the Normanist POV into his Mein Kampf.