ok, i'm not being egoccentric, i just wanted everyone to know that this theory is new to me, even if others have brought it up or discussed it before(i'm not ripping anyone off, in other words).
i recently re-watched the trial of a time lord, and this theory overwhelmed me, even though i'm sure they had no intention of this during the making of the episodes(at least i'm pretty sure it's not what they intended, all who shows are open to interpretation). the valeyard was created during the episode mindwarp, when the doctor's brain was worked on with that machine.
here's my theory: after the doctor's brain was "experimented" on, it opened a dark part of him. after the experiment in that episode, he started acting mean, and even during the trial, he couldn't remember what he had done. seeing as how the trial took place in time after mindwarp, that's how the valeyard existed. even in the next episode(the terror of the vervoids), the doctor was not himself. he would not put himself in danger, not rush to help. he was a different doctor from any of the previous 6th doctor stories.
the valeyard only existed because the 6th doctor's brain was messed up. when the 6th doctor regenerated into the 7th, the brain was healed, and the possibility of the valeyard no longer existed.
in the series we see specific things for each doctor. the 9th was angry and homicidal, being born out of the time war. the 8th was prone to bouts of amnesia. but we don't see these in the other doctor's because they are specific to each doctor. i say that if the the doctor's brain had not been experimented on in mindwarp, he would not have let perri die(i know she didn't, but c'mon, it was a better ending him not saving her), and the valeyard would not have existed.
i can even see close parralells between the 6th doctor and the valeyard. they both pride themselves on their intellect. they both put themselves above others(previous 6th doctor stories always had him fighting with peri, the worst relationship a doctor can have with a companion). the valeyard was the worst part of the 6th doctor, let loose.
what does anyone think? am i onto something here?