Short answers, pulled from the story.
Tengrism is a belief system originating on the Eurasian steppes, rooted in shamanism and animism, centered on the sky deity Tengri, whose name means "the sky" and may derive from a root meaning "daybreak" or "dawn." Adherents view the purpose of life as living in harmony with the universe. The highest group in the Tengrist pantheon consisted of 99 tngri, with 55 benevolent and 44 terrifying.
Tengrism was the prevailing religion of the Göktürks, Huns, Xianbei, Bulgars, Xiongnu, and Mongolic peoples, and the state religion of the First Turkic Khaganate, Old Great Bulgaria, the First Bulgarian Empire, Volga Bulgaria, Khazaria, and the Mongol Empire. Genghis Khan and his descendants practiced Tengrism until his fifth-generation descendant Ozbeg Khan converted to Islam in the 14th century.
The current spelling of Tengrism appears in the 19th-century works of Kazakh ethnographer Shoqan Walikhanov. French scholar Jean-Paul Roux introduced it into scientific circulation in 1956, and it entered English-language papers as a general term in the 1960s. The related term "Tengriianstvo" was introduced by Kazakh poet and Turkologist Olzhas Suleimenov in his 1975 book AZ-and-IA.
The most likely route of conversion ran through Sufism, where Dervishes were seen as akin to shamans. The Medieval Syriac historian Michael the Syrian noted that Turkic peoples found monotheism familiar because they had always proclaimed one sky god. The Kazakh ethnographer Shoqan Walikhanov observed that only the names changed: Gök Tengri became Allah and Tengrist spirits became div, peri, or jinn.
Mongol rulers invoked Tengri in letters to European kings and popes to assert divine authority over earthly rule. Arghun's letter to Pope Nicholas IV, dated the 14th of May 1290, placed Eternal Tengri as the final arbiter of whether Mongols would convert to any faith. Hulegu Khan's Latin letter to King Louis IX, dated the 10th of April 1262, refers to Jesus Christ as Misicatengrin, blending Syriac and Mongol terms.
In 2024, over one million people in Kazakhstan identified as followers of Tengrism, though the religion has not been officially recognized there. In Kyrgyzstan, about 50,000 people followed it as of 2014. It is undergoing organized revival in Buryatia, Sakha, Khakassia, Tuva, and other Turkic regions of Siberia, and continues in Mongolia alongside Tibetan Buddhism.