Archmistress of Magic

Once a powerful mortal wizard, she ascended to divinity soon after the God-Emperor and became one of the Living Gods who ruled over the Imperium the for next three centuries.

While the God-Emperor dealt with most aspects of ruling the empire, the Archmistress focused on Magic and Science and finding ways to harness them for the betterment of their subjects. As she rarely engaged with her subjects, there was an air of mystery surrounding the Archmistress and most commoners preferred to worship the openly benevolent God-Emperor.

When the demon hordes invaded the Imperial City in A.I. 400 the Archmistress fought the abyssal invaders and was devoured by the Demon Lords, similar to the God-Emperor.

The Woman Behind the God
Although the Imperium used all available resources to remove all mentions of the mortal lives of the Living Gods (since it is far easier to worship an all-knowing divine being than a fallible mortal), there are still quite a few elves around who lived before they attained divinity. Still, only those well-versed in history would know the original identity of the Living Gods.

Based on their recollections most scholars believe that the Archmistress of Magic was Princess Septima Augustus, archmage of the Arcane Directorium and sister of Emperor Octavius Augustus, who later became the God-Emperor.

Personality and Cult
Unlike the God-Emperor the Archmistress made little-to-no effort to win the hearts and minds of the people of Aegeron with her benevolence, and instead operated on a more transactional basis. Those who served her purpose were rewarded, those who stood in the way of her vision were moved either by words of force. Those who communed with her often described her as inscrutable and mysterious, always working towards some unknown long term goals.

She exercised direct control over the Arcane Directorium, and many of its members worshiped her. Unlike the common folk, the members of the Directorium had glimpsed some of the designs of the Archmistress, and came to believe that her orders are meant to ensure the long term safety of the Mortal Plane, although some scholars argued that the proof for this is quite limited (it should be noted that the Archmistress almost never censored scholarly opinions, which allowed these speculations to survive).

The Avalanche
The adventurers of the Avalanche learned that the Archmistress was aware of the prophesized awakening of the Great Old One and sealed its temples to prevent it. Unfortunately, with the death of the Archmistress the power of the seals faded, allowing foolish mortals to enter them.