The Tatars were part of the Asiatic hordes of Genghis Khan, which, in the thirteenth century, swept into Eastern Europe by way of Tatary, in Siberia. These tribes overran Asia and much of Europe, as far west as Poland. The tribes were ruthless and massacred anyone who opposed them. They caused devastation wherever they went. Legend has it that a Tatar would bite the hand of anyone holding him and devour anyone who let him loose.
The Tatars came to be called Tartars by the Romans, after Tartarus, the ancient word for hell, and there was no doubt that the Tartars made life hell on earth for the Europeans. Today, a savage, irritable or excessively severe person is called a tartar. The expression «to catch a Tartar» is to bite off more than you can chew, or to take on more than you have bargained for, or to struggle with an opponent who is extremely hard to handle.