If you want to get historical about it, the Romans ruled Crimea from around 15 BC until the 3rd Century sometime. After falling, successively, to the Goths, Huns and Khazars over the next few hundred years, it became split between Kiev and the Byzantines. The Mongols occupied large chunks in the 13th Century. The Genoese and Venetians also occupied areas. The Tatars conquered most of the Crimea in the 1400s and ruled it as a tributary state to the Ottomans. In 1783, the Ottomans ceded it to Russia after the Russo-Turkish War.
I say it goes back to the Mongols. Or maybe the Genoese.
To be honest I find Russia history confusing. As far as can tell their was the Moscow state and then Novgorod. Once Novgorod was soundly defeated Russia pretty much ran the gamut of what is now the Ukraine. There was no Ukraine in the early Russian empire, at least not as its own state. At some point I imagine it gained its own character. My point is I guess, is that being Ukrainian doesn’t seem to make one racially different from Russians. It was all the same peoples.