"Structure 10L-16 was the centerpiece of the Acropolis under Yax Pahsaj [the 16th and last ruler], as it had been since its establishment by the founder, K'inich Yax K'uk' Mo'. Investigations of the final phase structure by Acropolis Project Co-Director Ricardo Agurcia recovered thousands of fragments of façade sculptures that originally adorned both the temple at the summit, and the central and upper part of the frontal stairway, directly behind Altar Q.
Karl Taube and Barbara Fash have reconstructed the stairway sculptures and some of the temple mosaics in the new Sculpture Museum, with some surprising results. Like Altar Q, both the stairway and the temple refer to K'inich Yax K'uk' Mo' [Copan's founder], who is believed to be buried below this edifice, in the Hunal Substructure.
The bottom stairway sculpture panel shows an immense visage of Tlaloc, surrounded by a huge skull rack. Higher up on the stairs is the image of the founder, emerging from a sun shield. At the top is a large earth monster mouth, which Taube notes is decorated with highland Mexican mountain imagery, belching forth the figure of a bound captive. On the temple façades are six different kinds of depictions of Tlaloc, repeated numerous times.
The name of the founder was inscribed upon it, as well. Inside the temple, Maudslay found the pieces of a statue of K'inich Yax K'uk' Mo', which probably sat in the niche found at the back of the temple. Thus, Yax Pahsaj out-did all of his predecessors, even Ruler 15, in emphasizing the founder's ties to the great Tollan Teotihuacan. All later rulers of prominent Maya kingdoms, from the tip of Yucatán to the highland Quiché (as recorded in their royal genealogy in the Popol Vuh), would likewise claim descent from the royal houses of highland Mexico."
William L. Fash, Scribes, Warriors and Kings: The City of Copán and the Ancient Maya, p. 168-9