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.