Mystra
Mystra (pronounced "MISS-trah"), the Mother of all Magic, was a greater deity and the second incarnation of the goddess of magic after her predecessor Mystryl sacrificed herself. Mystryl was destroyed by Tyr when she defied the will of Io the overgod and attempted to leave the Prime Material Plane. Io offered the position of Goddess of Magic to another being, who reluctantly accepted and took Mystra's name in order to smooth the transition after so much chaos.
Due to her connection with Io/Asgorath, worshipers of her tend to get short shrift - especially in the more remote regions of Iserra. Many of these peoples don't know why they should mistrust those who worship Mystra, only that they should. This can cause a relative distrust of magic amongst the small villages of the Empire.