Yax Nuun Ayiin I was a son of Spearthrower Owl, a lord of Teotihuacan (probably that city's king) in central Mexico. The installation of a Teotihuacano noble on the throne of Tikal marks a high point of Teotihuacan influence in the central Maya lowlands. Yax Nuun Ahiin I may have been a child or youth at the time of his coronation, and the early years of his reign seems to have been dominated by one of his father's generals, Sihyaj K'ahk', in a sort of regency. Sihyaj K'ahk' is recorded as having entered Tikal on 15 May 378, the same date as the death of the previous ruler, Chak Tok Ich'aak I; it appears that this event may have been a conquest in which Yax Nuun Ayiin I was installed by force.