Co-creator deity paired with Xmucane; the divinatory grandfather of the Popol Vuh. Consulted by the makers Tepeu and Gucumatz at the third and fourth creation-attempts, his divinatory function is foundational rather than craftsman-creator (he does not shape the world; he reads it). Father of Hun Hunahpu and Vucub Hunahpu, grandfather of the Hero Twins. The day-keeper (ajq'ij) tradition still operative in highland Guatemala (Momostenango, Chichicastenango, Sololá) explicitly invokes Xpiacoc-Xmucane at session opening; this is one of the longest continuously-attested cult lineages in any New World tradition. The Tedlock (1982) ethnography of Momostenango establishes the unbroken transmission. Aspect-compounding with Hun-Ahpu-Vuch ("One-Hunahpu Possum") day-keeper title in some Postclassic sources, strengthening the calendrical-divinatory profile.