Sorry, but I don't think it's as simple and obvious as you all think. Given all the past retcons and twists, I don't think the answer to the Apprentice Xehanort/Terranort/Ansem issue will be something that you can base solely on the information or small details that are given at the moment. You need to think outside the square, and dig very deep into hidden symbolism. Get ready, this post will be very long, and I am probably going to go against the main consensus of most people in this fanbase.
Here is what is wrong with what you have written, Anagram, and most other people who have similar concepts.
Firstly, you are throwing the name "Ansem" around too naively. Young Xehanort himself stated that the figure in the brown robe, "who you
referred to as "Ansem", is
Xehanort reduced to just a heart". He doesn't say he is Xehanort's heartless, he doesn't say he is Ansem's nobody, Ansem's or Xehanort's dog or cat. He is Xehanort reduced to a heart. He even goes on to state that he was talking to himself, when Mr. Brown Robe is talking to Young Xehanort on the DI shore.
There is
no conclusive evidence to say that Brown Robe guy is the heartless that was created (if a heartless was even created) when Apprentice Xehanort, who had at that point taken up the name "Ansem", stabbed himself. You're all gonna jump on me now, but please keep in mind that Brown Robe guy has the power to transcend time
whenever he wants and can travel wherever he wants, since he has no bodily form.
Now, we have seen many times that Master Xehanort is able to cast out his own heart whenever he pleases. What if Brown Robe guy is actually just Master Xehanort's floating heart? We know he can cast it out, but who's to say that it needs a target? In fact, what needs to be put more into contemplation is how Master Xehanort was able to cast his heart out so many times? He cast his heart into Braig, Terra and even had the ability to do so
again in KH3D when he attempted to take over Sora. Not to mention, that when Lea blocked the heart, Master Xehanort was not even phased. He had just ejected his heart for nothing, but it didn't even seem to bother him.
Do you see where I am getting at? What's to say that Master Xehanort didn't just eject his heart into the open, creating Brown Robe guy? It wouldn't be too farfetched to assume this, as he can leap into whatever time frame he so wishes.
So now you are all going to be saying, why would Apprentice Xehanort/"Ansem" stab himself then?
I want to come back to the point about "Ansem" purposely doing it, in order to create nobodies for Xemnas to then prepare as vessels. No. It's not that simple. If this was the case,
please tell me why Braig was so shocked when he got stabbed? If this was all apart of the plan, i.e creating potential vessels for Master Xehanort's plan, why would Braig have been caught so offguard? More importantly, why would Braig even
need to have been stabbed, seeing as he
is already a vessel? Moreover, if Master Xehanort
truly had control over Apprentice Xehanort, why in the world would he stab Braig, and not to mention also pretend to have some kind of amnesia?
So what was "Ansem"/Apprentice Xehanort's
true motive then? Get ready to think a bit obtusely.
In the following, take a note of eye colour, something that has become very clear as a sign to tell who has a part of Master Xehanort inside them. Notice in multiple scenes in the most recent games, whenever someone asks some form of Xehanort, "Who are you?", it seems to zoom in on their eyes, without them answering. This happens when Aqua asks Braig who he is at the Keyblade Graveyard in BBS, and when Riku asks Young Xehanort who he is in KH3D during his first Traverse Town visit.
Here is Terranort:
Eye colour: Yellow, clear Master Xehanort influence. Notice how in this scene too, it zooms in on Terranort's eyes immediately after showing his face.
Here is Braig/Xigbar:
Eye colour: Yellow, clear Master Xehanort influence. Notice the camera zooming again.
Here is Apprentice Xehanort, as seen in Blank Points, and the painting of him in Radiant Garden:
Eye colour: Brown. No Master Xehanort influence, however the origin of his eye colour is something that should be considered, however I won't delve into that yet. What I find is most important to talk about is...
Here is Ansem the Wise:
Eye colour: Amber/Orange. I chose this scene in particular due to the significance it has in my proof.
Immediately after this zooming in on Ansem's eyes, which as I said before holds significance, it skips to this:
And it zooms out from his eyes.
Please take a look at how Ansem the Wise is seated:
Now, here is Xemnas:
Eye colour: Amber/Orange. Do you see where I'm going yet?
Further, here is Xemnas at the dark margin. Please take a look at how Xemnas is seated:
Apologies for the quality, but do you see how very similarly both Xemnas and Ansem the Wise are sitting? Most people will dismiss this as coincidence, but do you also find it coincident that Xemnas chose his name as a pseudonym of Ansem rather than Xehanort? Or how, in his later moments, Apprentice Xehanort chose his name as "Ansem" instead of Xehanort?
Just one more, here is Ansem, Seeker of Darkness:
Eye colour: Amber/Orange.
Both Ansem Seeker of Darkness and Xemnas, the "proposed" nobody and heartless of Apprentice Xehanort both share what in common? Yes. Eye colour.
Now every time Master Xehanort has taken over someone, their eye colour changed to the same colour as his, the yellow. For example, Braig and Terranort.
Well, guess who Ansem SoD and Xemnas also have common eye colour with?
Yep. Ansem the Wise.
But what does this mean?
As we have been told, Apprentice Xehanort (with brown eyes) was very keen on researching the heart, and was severely disheartened when Ansem the Wise did not let him continue his research.
Why Apprentice Xehanort was so keen on researching the heart may be discussed, as to who had control of him at this time, and there is not much evidence for Apprentice Xehanort's to conclude upon, thus this here is open to contemplation. However it
is clear that he is not under Master Xehanort's influence at this stage, due to his eye colour. It is very, very hard to conclude who had control of him at this stage. One potential theory that I am inclined towards is that he had nurtured his own heart by this stage, locking away both Terra's and Master Xehanort's hearts (also Eraqus), as Xemnas reiterated is possible in KH3D ("Once born, a heart may also be nurtured...") and deep down had the memories of Terra, Master Xehanort lodged inside him. I believe that right after Ansem the Wise found Terranort, where he stated his name is "Xehanort", Terranort, or Apprentice Xehanort, was much akin to the Lingering Sentiment, where by accidentally locking his heart(s) away, inside he contained none, however he still had the lingering emotion of incredible hatred toward Xehanort, and that is all he could remember at that time. Later, as he nurtured his own heart, he began to question who he truly was.
This could especially be the case considering that Braig would constantly be reminding him of his former self, as seen in Blank Points. "Come on! Please tell me the amnesia was a sick joke..."
So, after being stopped by Ansem in his research, Apprentice Xehanort, perhaps discovering more and more about himself through the research on the heart, did not want to conclude the research. At this stage, he may have discovered things about himself like being able to wield the keyblade, and the dark realm, or perhaps he had some lingering memories from Master Xehanort and Terra come back to him, where by using this knowledge, and with the help of the other apprentices, he was able to banish Ansem the Wise to the Realm of Darkness.
Despite all this above, which is very ambiguous, I think the next part of my theory is a bit more concise.
After being banished to the Realm of Darkness, his 1st visit, Ansem the Wise had, perhaps, even more darkness in his heart than Master Xehanort himself due to the sheer amount of rage and hatred that he felt for Apprentice Xehanort, who banished him. He even states this himself, obtaining the power of darkness and naming himself Darkness in Zero, ready to get his revenge. The
extent of his revenge, I believe has been hidden from us throughout the whole series, and is actually the reason for the mistaken identity case of Apprentice Xehanort/"Ansem".
Acquiring the power of darkness, Ansem the Wise (now DiZ) sets off to confront Apprentice Xehanort. His intention was probably to kill(banish) each and every apprentice. The easiest way to do this was to take control of the now leader of the research among the apprentices, Xehanort. So like Master Xehanort, using his newly found power, he extrudes his heart and takes control of Apprentice Xehanort's body. He is able to successfully do this due to the extreme darkness present in his heart, and due to Apprentice Xehanort's already dark background. He then takes out the other apprentices with Apprentice Xehanort's keyblade, in the intention of banishing them, much like he was banished. And this is what we see at the beginning of KH3D. It would explain why Braig was so shocked when he said "My name is not "Xehanort"", and why he would say his name is "Ansem". Because it actually
was Ansem, getting his revenge. And what better way to do it than to mutter, just as Braig is on the verge of fading away, "My name is Ansem."
After banishing all the other apprentices, he stabs himself, believing he will rid the world of Apprentice Xehanort and get the revenge he wanted, at the cost of his life. However as we all know, after stabbing himself, he would bring an even greater evil among the world in the form of his nobody Xemnas and his heartless Ansem SoD. Furthermore, having stabbed himself, without knowing it, he arrives in the Realm of Darkness a second time. Throughout all this, as he travels around in the Realm of Darkness, he begins to feel remorse for what he had done, perhaps he finds out from sources, namely Mickey, within the Realm of Darkness what is happening in the Realm of Light. He knows he is responsible for it, and he feels compelled to do something about it. Mickey also tells him about Riku, who had been possessed by a figure named "Ansem" which, again, is Ansem the Wise's fault. So, Ansem the Wise begins his agenda to repay the world, by helping Riku remove the darkness inside him, as seen in Chain of Memories. This would also explain how Ansem the Wise was able to alter his appearance to look like Ansem SoD for the beginning of Chain of Memories.
This is why throughout all of Kingdom Hearts 2, he always says he is a "fool" and everything that has happened is a result of his revenge. I never saw Ansem the Wise's revenge agenda to be of such fatal consequences to the world, as his revenge is described in KH2, however considering all of this, and how he could potentially be the root of all problems, he may even be considered the 2nd antagonist of the series. He even planted data inside Sora, as we find out in KH3D! Why would he go
so far in an attempt to save the world? What he must of done
surely was absolutely atrocious, and this theory supports just that motive.
Further to this, notice when Braig refers to the plan to create 13 vessels in KH3D, he says "
Xemnas and
Xehanort formed the Organization for a specific reason..."
Why would he refer to Xemnas and Xehanort as different people, if in fact, they were both one and the same? (Xemnas being Xehanort's nobody would make him Xehanort too, technically)
After the events of KH2, as a second sacrafice, this time to save the world, Ansem the Wise blows himself up with the machine that he uses to destroy the artificial Kingdom Hearts. However, this is not when he arrives in the Realm of Darkness. Once Xemnas is defeated, Ansem the Wise is reborn, due to his heartless half and nobody being defeated, in the Realm of Darkness, his 3rd visit, where he then later meets Aqua at the Dark Margin, as seen in Blank Points.
This may seem a bit farfetched, but it seems possible to me. Please tell me what you think, and I will try to expand more on points that may be a bit vague, as this post is already way too long, if there are any questions. I know I should of made my own thread, but I found this topic to be a great opportunity to finally voice my opinion on this matter.