The test-tube Empress
Also know as The One, Empress Annarette the First.
Annarette was the daughter of the God-Emperor of Mankind, probably born in early M31, before the Horus Heresy. She is the only known female offspring of the Emperor. She has strong psychic ability as well as other genetic improvements, but not to the same extent as what the Primarchs had.
Annarette became wary of her father’s paranoia towards psykers and started fomenting a plan to save them. She organized a major exodus, both of psykers and regular humans, towards the most far-flung sector of the galaxy, which we now know as the Handar Expanse. There, they settled the Pyr Colony in secret, away for the Imperium of Man.
She did not live to see that plan come to fruition, as her father murdered her in unclear circumstances. Her gene-seed was somehow preserved however, and ended up in the custody of the Necrons for the next 10 millenia, until it was recovered by the Rogue Traderand his crew.
It took tech-priest Divis most of a year to unlock the secrets of that Gene-seed and bring Annarette back to life. Once revived, Annarette wasted no time in fomenting a plan for revenge on her father. Canoness Superior Arabella and the High Lords of the Pyr Colony swore allegiance to her as Annarette the First. And there was much rejoicing.