This paper primarily focuses on the highest deity, the Upper Thearch of the Nine Heavens (officially translated as 'The Supreme God of the Ninth Heaven'), in the Korean new religious movement (NRM) Daesoon Jinrihoe and the true minister of the myriad spirits in the Taiwanese NRM, Yiguan Dao, the Upper Thearch of Manifest Luminosity. As the two both serve as highly representative "Upper Thearch" beliefs in emerging NRMs, I attempt a comparative analysis of the source of these beliefs, their characteristics, and the links that exist between them. On the basis of ancient Chinese classics and Daoist texts, along with Daesoon Jinrihoe's scriptures and works from Yiguan Dao's Canon, I try to understand the distinguishing features of cosmological ideas from both religious movements. For example, because the Upper Thearch of the Nine Heavens could not bear to see the human realm growing ever more disordered and in order to improve worldly conditions, he traveled to the harmonized realm of deities, and therefore descended into the world to make a great itineration and enlighten the people through his teachings. In the end, he came to Korea and was reborn as Kang Jeungsan (secular name: Kang Il-Sun) in Gaekmang Village. In the Human Realm, he spread his transformative teachings to the people which were later became the doctrines of the Virtuous Concordance of Yin and Yang, Harmonious Union between Divine Beings and Human Beings, the Resolution of Grievances for Mutual Beneficence, and Perfected Unification (jingyeong 真境) with the Dao. Yiguan Dao; however, explains that the source of humanity is the "Heaven of Principle" (Litian 理天), and people are "Buddha's Children of the Original Embryo" (Yuantai Fozi 原胎佛子), created by the Upper Thearch of Manifest Luminosity, who came to world to govern and impart spiritual refinement, before returning to his native place in the Heaven of Principle. Yet, because he became infatuated with the world of mortals, he forgot the path of his return. Therefore, the Eternal Mother sent Maitreya Buddha, the Living Buddha Jigong 濟公, and the Bodhisattva of Moon Wisdom (Yuehui pusa 月慧菩薩) to descend to the human world and teach the people, so that they may acknowledge the Eternal Mother as the root of return, achieve their return to the origin, and go back to the home of the Eternal Mother in the Heaven of Principle. Both Daesoon Jinrihoe and Yiguan Dao refer to their highest deity, the true ministers of the myriad spirits, with the simple title "Upper Thearch." This phenomenon also has some ties to God in the western Biblical tradition but also has some key differences. In investigating the sources of these two deities, we find that they likely took shape during the Yinshang (殷商) period and have some relationship to the Upper Thearch of Chinese antiquity. The questions raised in this research are quite interesting and deserving of deeper comparative study.