Yrro was the mythological creator of the S'pht, who revered him as a god[1].
According to S'pht mythology, he and his cohort Pthia fled the W'rkncacnter and settled upon the desert world of Lh'owon. They brought with them the S'pht, who they used to terraform the planet to their desires. However, when the W'rkncacnter came and led to the death of Pthia, Yrro flung the W'rkncacnter into Lh'owon's sun. Grieving the loss of Pthia and believing he had failed his creations, he scattered the S'pht into eleven clans and tasked them with maintaining Lh'owon in his stead.
Notes
According to Chris Geisel (a dev at Bungie and later Double Aught), Yrro is an alternate spelling of Jjaro[2]. It is likely that Yrro is related to the Jjaro in some way, either being a Jjaro himself or being a mythological representative of the species as a whole.