The true origins of Aesmandroth are unclear. He is referred to as the “Son of Azura”. Legends name the House Azura patriarch Daon as his father but some argue that he was a mortal who ascended to daedrahood after being blessed by Azura. Whatever the case, Aesmandroth is a half mortal / half daedra demiprince with respectible power. Although his mortal blood makes him more vulnerable than his daedric kin, his unique lineage gives him a particular affinity with the mortal plane of Mundus. This mortal connection combined with his inherited ability from Azura to bypass liminal boundaries between realms (see ‘Words of Clan Mother Ahnissi’ and the First Secret) has given Aesmandroth a particular skill at passing through these boundaries or making pathways for other et’Ada.
Aesmandroth’s mortality never fit into Azura’s picture of beautiful perfection which she prizes so highly. And his dabbling with opening holes into her realm became problematic. So he was cast out of Moonshadow. During his exile, he pondered the frailness and limits of mortal existence. He saw how mortal souls were doomed to fade away after death and contrasted this with how a daedric animus was anchored to Oblivion; able to return to their origin after being banished. So it was that he formulated a plan to merge daedric animus with mortal souls. He would anchor these hybrid beings to himself so that even in death, they would return. He soon found that this solution was imperfect, many souls were driven mad by lunar radiation as they passed through the lattice after death to meet him in Oblivion. The liminal boundary between Mundus and Oblivion could be bent to allow the mortal-daedric beings to pass through, but not without side effects. The souls frequently came through fragmented, like the lattice were a metaphysical object which sliced the daedric portion of themselves to pieces.
After drifting aimlessly in the voidstreams of Oblivion for some time, he eventually formed his own realm from which to execute his plans. By this time, he had devised a solution to this failure. Recognizing that he was an imperfect anchor while residing on this side of the mortal realm, Aesmandroth believed that in order for his children to thrive in perpetuity, they needed something more stable. His thoughts were cast to Nirn herself, and the laws which governed the mortal realm. He resolved that he would sacrifice himself to become a new earthbone, one representing a soul anchor for mortal souls with the appropriate attunement to maintain their identity within the mortal realm without needing to flee to Aetherius, Oblivion, or any external point of origin. But to accomplish this, he needed a stronger bond to the mortal realm. The Convention from the elder days has solidified the physical, temporal, spiritual, and magical elements of Nirn in place. Great skill is required to manipulate these earthbones, and greater skill yet to permanently add to or subtract from them (see Mannimarco and the Necromancer’s Moon). This meant that Aesmandroth would need many followers and/or sacrifices to fuel his power in Nirn. So the cult was formed.