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.
Elizabeth Hill Boone, Painted Architecture (1985), 132.
the name of a deity associated with the creation of the sun
Fr. Bernardino de Sahagún, Florentine Codex: General History of the Things of New Spain; Book 7 -- The Sun, Moon, and Stars, and the Binding of the Years, Number 14, Part 8, eds. and transl. Arthur J. O. Anderson and Charles E. Dibble (Santa Fe and Salt Lake City: School of American Research and the University of Utah, 1953), 4.