We do not know who Genghis Khan was by nationality. Some scholars suggest that he was a Turkic Aryan from Kashgar, others (such a majority) consider him a Mongol.
But we can say for sure that Genghis Khan never belonged to the Tatars. The Tatars, in contrast to the Mongols and their modern descendants - Buryats and Kalmyks, belong to the Turks, and throughout the life of Genghis Khan, they were his blood enemies.
It was the Tatars who poisoned Chinggis's father when he was only nine years old. The description of Genghis Khan's appearance gave rise to doubts about his Mongolian origin. Red hair and gray-green eyes, unusual for the Mongols, distinguished him among his fellow tribesmen. However, these data are gleaned from an essay written half a century after the death of the conqueror and trust them (unless of course we are not talking about a genetic mutation) should be very careful.
Strictly speaking, Genghis Khan is not a name, but a title. He was received by Temujin at a kurultai (meeting with the Mongols) at the end of the 12th century. A few years later, in 1206, now at the big kurultai of all Mongol tribes, the title of Genghis Khan, emphasizing the primacy, was confirmed by all the Mongol princes. The meaning of the title "Chinggis" is dark: "Chinggis" or "Tengis" the Mongols called the sea, it was a separate deity in the pantheon of shamanism. Perhaps it is associated with the name Tengri - the god of all Mongols. The anonymous author of "The Secret Legend of the Mongols", and translates Genghis Khan - Khan by the will of the Eternal Blue Sky. And the name given to Genghis Khan at birth is Temujin, which means "blacksmith". It is related to the Turkic-Mongolian root "temur" - "iron".