Perhaps most interestingly, what little we know of their religion and government suggests that the polity has reconciled the typically opposed forces of Good and Evil. Before becoming a Squire, Catherine Foundling once served a Yan Tei missionary, suggesting they have their own religion not based on the House of Light nor the individual worship of the Gods Below. Their highest seat of power is shared by a Hero and a Villain.
The people of Yan Tei are said to have honey-coloured skin and are famous for their sealing arrays - both the protective and sealing types - to the point where Black Knight uses them to protect his property in Ater.
Nothing has been revealed with regards to their origin and the little scraps of history we have are usually related to Calernia.
It's believed they landed a punitive expedition on Praesi shores, back in the days of Dread Empress Triumphant and captured many of the devils and demons used by her forces. One of them might have been a Demon of Absence as they allegedly haven’t been mentioned for roughly two hundred years in any of the Calernian records. Their sudden disappearance and reappearance suggests this was accomplished via magical means, as does the fact that people hadn't event noticed the records were incomplete.
We're unsure how this lines up with the claim that a Demon of Absence is still sealed inside one of the Imperial Standards hidden near Harrow. It's possible this claim is false or that the Demon is not a singular entity.
At some point, Yan Tei waged war against Teoteul and won. The Teoteul might be the so called "tigermen" though they have only been mentioned a couple of times.
Yan Tei is the only polity which has the records on the city of Kerguel which heedlessly pursued knowledge of physical sciences despite receiving two Red Letters. Kerguel was eventually destroyed by Gnomes.