Green’s Dictionary of Slang

tartar n.

[proper name Tartar, an inhabitant of the region of Central Asia extending east from the Caspian Sea, and formerly known as Independent and Chinese Tartary; ult. Persian Tatar, but linked in Western ears and superstitions with Lat. tartarus, hell]

1. [late 16C–18C] a strolling vagabond, a beggar, a criminal mendicant.

2. [late 16C–1940s] (also tart, tarterer) a general derog. description.

3. [late 18C–19C] a champion, an expert.

In phrases

catch a tartar (v.)

[late 17C+] to encounter an apparent victim or weakling who turns out to be much stronger than suspected.