Over the span of some two hundred years, from the late Western Han to the late Eastern Han, triad images featuring a prominent central being flanked by two smaller, snake-bodied figures, occurred on murals and carved stones in Henan, Shandong, and adjacent areas. The iconographic schema of the flanking figures, Nüwa and Fuxi, appears mature and stable, with their identities consistently determined by their half-human, half-serpent, and gendered bodies as well as by the divine objects they hold—sun and moon, compass and T square, numinous mushrooms. The iconography of the third being, however, appears far less consistent and somewhat elusive, yielding many different identifications by scholars. The seemingly anomalous pictorial program speaks to the issue of iconographic volatility in Han art. Looking across the corpus of triad images, this essay identifies the volatile third being as the Grand One, and proposes that its figural metamorphoses were predicated on the amorphousness of the supreme deity of Daoist cosmogony. Distilling the three most important formal aspects of the Grand One—a therianthropic being, a forceful facilitator, and a regal icon—this essay argues that the triad images embodied a coherent program depicting the cosmogonic origin of the world that began with the Grand One conjugating yin and yang, associated with Nüwa and Fuxi respectively. The emergence of this triad imagery coincided with evolving Daoist thought during the Han dynasty.