Nun Yax Ayin was a king of the most powerful state of classic Maya civilization, Tikal in the late 4th century.

He was sometimes referred to by the name King Curl-Nose or Curl-Snout before the hieroglyphs for his name were deciphered phonetically.

He took the throne of Tikal on 13 September, 379, soon after the death of previous king Jaguar-Paw, apparently in battle.

Nun Yax Ayin was a son of Spearthrower Owl, a lord of Teotihuacan (probably that city's king) in Central Mexico. The instalation of a Teotihuacano noble on the throne of Tikal marks a high point of Teotihuacan influence in the central Maya lowlands.

Nun Yax Ayin may have been a child or youth at the time of his corrination, and the early years of his reign seems to have been dominated by one of his father's generals, Siyah K'ak', in a sort of regency.

His tomb, known as "burial 10", was discovered by University of Pennsylvania archeologists.

He was succeeded as ruler of Tikal by his son Siyah Chan K'awil, probably in 411.