BG3 SPOILERS! Turn back now if you don't know about Ansur or that scene with Stelmane.
Below is the story as told by the Emperor, along with screenshots showing the extended/altered versions related to Ansur (green), Stelmane (red) and some extra notes/books (orange). It doesn't explore Stelmane's case in detail.
All of this is already covered in our FanDoc, just reorganized here in a slightly less boring way.
"I was someone once. Someone just like you. An adventurer. I came from Baldur's Gate, though I was never one to be constrained by circumstance. [0]
It's like I always told you - I was just like you. An adventurer who yearned for greatness. And in mortal terms, I achieved it. As Captain of the Wandering Eye I acquired enough gold to found Baldur's Gate. [1]
Ansur was my friend. We crossed the Calim together and sailed Yal Tengri. We built a city by the sea." [2]
Balduran, a sailor of exquisite renown who founded the city of Baldur's Gate many years ago. […] claimed a guardian and friend, Ansur. [A]
Astarion: Balduran sails off into the sunset, leaving the dragon to look after the city. Lazy git. [5]
"I longed for more. [0]
I stayed for a while, to watch my city grow, but it was not enough. I grew restless again. The sea called to me, and I ran to her with open arms." [1]
[Cine: moving still of the ship in the middle of a cataclysmic storm]
"My ship was destroyed, my crew lost, but my spirit was far from broken. I was determined to return in triumph once again." [1]
[Cine: A boot stomps on a jutting piece of land (like the final step to get to the top of Everest.) The other boot follows. The adventurer has stopped there. A map in his hand. He's arrived: Moonrise Towers (before the shadow-curse.)]
[Cine: Moving still of Balduran walking away from a shipwreck / towards Moonrise with a map.]
"That longing brought me to Moonrise Towers on a search for treasure. [0]
I heard of treasure in Moonrise. I strove to find it." [1]
[Cine: Moving still of Balduran being tadpoled.]
[Cine: Cut to: mind flayer approaching the back of a board on which the adventurer is strapped and struggling. The mind flayer carries a tadpole (throwback to intro cinematic.) Closeup of the adventurer's eye as the tadpole goes in. Fade to black to screams of the adventurer. Fade in: Shot of the same room, clasps being undone on the board. A naked mind flayer rises - the Emperor.]
Emperor: In my original humanoid form, I possessed an exceptionally strong personality - so much so that even after ceremorphosis I was still substantially 'myself'. [B]
"To a colony of mind flayers who caught me, changed me into what I am now. [0]
What I found was an illithid colony, where I acquired a tadpole much like yours, and became a mind flayer, enthralled to the elder brain." [1]
Of course, I concealed this beneath a semblance of perfect servitude. […] Thirteen and three-quarters years. [B]
"For years I served the elder brain - the one you know as the Absolute. I was a thrall like any other." [0]
Gortash: Until finally you were given a mission to Baldur's Gate, distant enough to be out of the elder brain's control [B]
[Cine: Shot of elder brain, psionic charges emanating off it, connecting to legions of mind flayers. We see our mind flayer walking at night, cloaked, down a street in the city. It looks around to make sure it wasn't followed, before disappearing through a door.]
[Cine: Still of Ansur frantic. Moving still of Ansur pulling mind flayer Balduran from the hivemind. | Anim: Pulled either via magic or physically. Need further confirmation]
"But I was fortunate. I broke free, and started a new life in my old city. [0]
It was Ansur who found me, Ansur who pulled me from the brain's domination, Ansur who brought me home." [1]
"When I first escaped from the elder brain, I searched for a new vessel. But the longer I inhabited this one, the more it grew on me. *
I realised that returning to my former self would only impose limitations. " [0]
[Cine: A prison. Shadows flit over the prison's walls by candlelight. A scream. Shot of mind flayer, wearing the garments we later find in the Elfsong Tavern (garments that disguise its true form) suckling on a criminal's brain in its cell. The door has been broken open by its psionic strength.]
"I sustained myself on criminals. Unglamorous, but there were plenty of them, rarely missed, and they fuelled me while I did my work. [0]
… my meals - villains and lawbreakers. You see I tried to exercise morality, where I could." [3]
[Anim: Mindflayer on bed, Ansur at door with healer panic]
"He sought to cure me of my sickness, called on every healer he could find, nearly broke his spirit in the attempt. But he failed to understand - I wanted no healing. I was not sick. [0]
I was on the cusp of greatness beyond my wildest dreams. [1]
Ansur: You were becoming illithid." [4]
Be free, Ansur. Fly. And know that even if I'm not beside you,
I will always have been your Balduran. [D]
Ansur: I offered you merciful death; you chose to fight. […] you repaid me in slaughter. [4]
"He came to me as I slept - a mercy killing, in his mind.
I saw the tears - I felt his grief. I had no choice but to kill him first - it was an act of self-preservation." [1]
… after a betrayal too piercing to recount here in worthy detail, Ansur fled beneath the stone, thereby changing the name of the region he now slumbers under to match his draconic lineage. [A]
PART 2 - Duke Belynne Stelmane
"People referred to me as the Emperor - such was my influence. Though, of course, they had no idea what I really was." [1]
It was introduced to me as 'the Emperor.' Surprising.
But its information was good; its ideas, brilliant. I'll not turn up my nose. A boon to the Knights, I think. [E]
[Cine: Emperor in Stelmane's office, colluding with her over a big map of the city on the table. While we look at the map, the ‘reach' of the Knights of the shield is visualised across the map as more and more regions come under their control. | Stelmane conducting business with a merchant.]
"I had the good fortune to meet Duke Stelmane.
We formed a partnership, and through her I became the governing force behind the Knights of the Shield, the largest mercantile operation in Baldur's Gate." [1]
[Cine: We see Stelmane lying in a coma in her bed. Shot of her eyes moving left and right under the lids, a struggle painted all over her face. Background becomes black - we see the Emperor standing over her bed in the same scene, dominating her mind with psychic energy. Shot of Stelmane's eyes blinking open, possessed.]
"In life, she was my business partner. Back when we ran
the Knights of the Shield. A difficult task, for a mind flayer.
Duke Stelmane trusted me, and the city trusted her." [6]
[Cine: Moving still: Stelmane and a merchant in conversation. Through a gap in the door behind them, the mind flayer's eyes glow.
Shot of merchan'ts unease. Shot of Stelmane's face - eyes rolled back like Orpheus', clearly possessed. NB this is the same as the scene in INT_EmperorRevealed_AfterOrpheus but with the added reveal of Stelmane's possession.]
"I conceived the plot, but Belynne took centre-stage. It was she who met with the merchants, politicians, patriars. It was she who negotiated deals and signed off on agreements. [6]
"Her rooms played host to the most important conversations in the city. Together, we brought order to chaos. At its height, everything that happened in that city went through the Shield. Through us. [1]
My end is and has always been freedom. Belynne understood this. Belynne became my freedom." [6]
Though Stelmane shows evidence of increasing debility due to some sort of wasting disease, her influence over transfer of contraband in the Gate has only grown as her physical abilities have declined. Solving this enigma should give us the key to bringing down the Knights. Investigations continue. [N]
[Cine: Emperor and Stelmane toasting to their success in her office. (Emperor's drink should probably look like brain parts rather than humanoid alcohol.)]
"My needs were sated. I was… happy. For a while." [1]
… 'the Emperor' a suspected [REDACTED], has been exerting an undue amount of power over influential actors within the city, including members of the ducal council …
If this 'Emperor' really is a [REDACTED] we must
take swift action to ensure [REDACTED] has not become [REDACTED]. [I]
Negotiations with prospective clients have proven so difficult that we now believe the Knights exert some sort of influence […] psychic [F]
[Cine: A bang as the door bursts open. They both look at the door in horror.]
"Until my true nature was discovered by the tyrant himself - Lord Gortash." [1]
Nuge - In the Knights' secret chambers […] The secret part, yes. That's where she found me […] it found me. At first I thought she was blue and floating, but then it was just Stelmane. She smiled. I don't remember anything after that. [G]
[Cine: Shot from Emperor's POV of chains and magic lashing, binding him. Blurring in and out as if fading in and out of consciousness. Next conscious moment: staring at the stars through bars on the back of some sort of horsecart. Next conscious moment: the mind flayer colony coming into view. Mind flayers turn to stare. Next conscious moment: the elder brain, and beside it, Gortash.]
"He tore me from my home and brought me back to the brain where I became a slave once again." [1]
Can't explain the relapse. Duke lacks appetite, awareness, or interest in anything. Occasionally asks after visitor, which I suspect might be cause of current condition. [H]
[Cine: Shot that pans out from the Emperor, showing it to be one among many (though wearing its distinctive garb). Non-mindmeld Emperor's hand waves, wiping away the image, revealing it standing there before us. Mindmeld over.]
"A slave he continued to call the Emperor. The name was intended as a slight - to remind me of the heights from which I fell." [1]
The former black market leaders, the Knights of the Shield and (outside the city) the Zhentarim, have largely been supplanted by Gortash's operation. [K]
[From Gortash] Thus was born the plan to send a tadpoled strike team in a regrown nautiloid piloted by the Emperor to steal the Astral Prism from Vlaakith. [J]
Emperor: I am entirely devoted to the needs of our
elder brain and of its masters. [B]
The Netherbrain: When the Chosen sent my thralls to retrieve the Prism - who do you think let the 'Emperor' slip its leash, knowing it would be the one to bring you to me? [7]
"The moment I found it, I felt a change. My free will
returning. I followed the feeling inside - And found Orpheus.
While my body was within the Prism's bounds, my mind was free. I could resist the elder brain, the Chosen. Better yet, I could plan to overthrow them." [1]
An anomaly. One like ourselves, unconnected from the whole. Caution. [L]
"All I needed to do was subdue Orpheus and find allies in the outer world. You." [1]
I studied you. Your motivations, your actions, your desires.
I deduced the best way to align your goals with my own." [9]
Shadowheart: After they put that tadpole in my eye, I heard this voice. It was… soothing. […] The voice said I'd become a 'beautiful weapon'. [10]
[From Gortash] The body of our handpicked captain for the artefact raid wasn't found in the wreckage of the nautiload, and I'm not at all easy in my mind about that fact. [M]
* The Emperor tweaks how it speaks depending on how much Tav resists, hinting at its transformation. Not diving into that here - it needs a proper deep dive.
I'm using intro cinematic images here since they flow well with the narrative, however, Larian never resolved the conflict about the tadpoler's identity.
++ St
-- Sources --
[0] INT_EmperorRevealed_AfterOrpheus
[1] WYR_AnsurGhost_HelmetPickup
[3] LOW_Elfsong_EmperorAD_EmperorPrisonerChains
[4] WYR_AnsurGhost_HelmetPickup
[5] WYR_Wyrmway_Mural3_PAD
[6] CAMP_DaisyStelmane_AvD
[7] END_MorphicPool_NetherbrainConfrontation
[9] CAMP_DaisyAcknowledgement_AvD_ROM
[10] CAMP_Night2_CRD_Shadowheart
[A] Balduran Founds a City
[B] Evading the Elder Brain
[C] Emperor's Missive ([B])
[D] Dear Ansur
[E] Journal
[F] Knights of the Shield Report
[G] Shield Steward Interrogation Log
[H] Patient Log: Duke Belynne Stelmane
[i] Crumbling File
[J] The Astral Prism Heist
[K] Inroads by Arms Dealer Gortash
[L] TUT_Lab_PAD_MFBook
[M] Accelerated Grand Design
[N] The Stelmane Connection