Elizabeth Hill Boone notes how the Florentine Codex, Book 7, "says that Nanahuatzin was the syphilitic god who thew himself into the flames and became the Fifth Sun." And "Thompson says that Nanahuatzin and Xolotl were interchangeable." She also notes how "Seler regards Xolotl as the canine god who conducted the sun each evening through the underworld." She adds "Xolotl might also be considered the sun as well as Venus." She thinks Xolotl is Venus as the Evening Star but also the Venus of the underworld.
the name of a deity associated with the creation of the sun
Auh in nanaoatzin, in jacxoiauh, muchi çan aacatl xoxouhqui, acaxoxouhqui, eey tlapilli: tlacuitlalpilli, nepan chicunaui, in ie muchi: auh in içacatapaiol, çan ieeh in ocoçacatl: auh in iuitz, çan ie no ieh in meuitztli: auh inic quezhuiaia, uel ieh in iezço: auh in icopal, çan ieh in inanaoauh concocoleoaia. = And [as for] Nanauatzin, his fir branches were made only of green water rushes -- green reeds bound in threes, all [making], together, nine bundles. And his grass balls [were] only dried pine needles. And his maguey spines were these same maguey spines. And the blood with which they were covered [was] his own blood. And [for] his incense, he used only the scabs from his sores, [which] he lifted up. (central Mexico, sixteenth century)
Elizabeth Hill Boone has said that Nanahuatzin was "the syphilitic god who threw himself into the flames and became the Fifth Sun." Xolotl and Nanahuatzin have a close relationship and Thompson has suggested they are interchangeable.