By critically examining historical accounts of a powerful proto-Tibetan king, Yao Xing, who replaced his regal title huangdi (emperor) with tienwaig in 399 CE, in an official history, Book of the Jin (completed in 644), the article determines that tieiwang actually refers to Śakra/Indra, the ruler of Trayastriśā Heaven, often called as devarāja(king of gods), representing the Buddhist ideal king, rather than the Confucian concept of tiemwang (heavenly king) as suggested by other scholars. The article argues for this explanation with materials from various sources: the Buddhist conception of Śakra/Indra in the scriptures and sculptures that were then circulated in China, Chinese Buddhist records on Yao Xing, and the Buddhist usage of devarāja in the regions other than China. For Yao Xing's regime was short-lived, the article reaches the conclusion that Buddhism's political operation in the name of devarāja was essentially incongruous, and therefore unworkable, with the existing Chinese statecraft.