I first read about Tatars in tales by Tolstoy set in Crimea. For many centuries Ukraine mostly consisted of Cossacks in the North and Tatars in the South. Both groups were tremendous fighters.
Tatars are today the largest minority group in Russia.
About 900 years ago, the Golden Horde (Mongols led by Genghis Khan) overran Russia, Ukraine, Georgia, etc. Most of the Horde eventually left, but among those who stayed were the Tatars, a mix of local people and the original Tatars, whoever they were. They converted to Islam, joined the Ottoman Empire and ruled Crimea for many centuries. At one point the Crimean Tatars sacked Moscow and burned it.
In 1944 Stalin rounded up the Crimean Tatars and shipped them east and out of sight. About 25% died during the trip and exile. Russians confiscated their land and homes. Later Gorbachev allowed the Tatars to return to Crimea, where today they are a minority.
I'm guessing that descendants of the Tatars and Cossacks are not fond of the Kremlin.