This is very SPOILERY Dragon Age meta that is exploring a possibility that I was thinking about a few months ago, and only found in my drafts now. I think that there are still Reveals that are yet to come about Solas because he’s still suggesting that you’ll have “questions” for him, and there are a few possibilities of what those reveals could be, and this is one of the more likely possibilities.
This depends on the theory that Solas was originally a spirit, so if you don’t agree with that theory this won’t have legs for you, but maybe you’ll find it interesting.
So given established lore, if you draw a Wisdom spirit from the deepest Fade and you bind that spirit and charge it with something opposed to its nature/original purpose—fighting, as extremely clearly defined specifically in Solas’ personal quest —
(or “it started with a war,” as Solas describes while grimacing in Trespasser, and also “he did not want a body, but she asked him to come. He wanted to give wisdom, not orders”)
— that is exactly how you corrupt a wisdom spirit into (specifically) a pride demon.
So if that’s the case, and if Solas was originally a wisdom spirit
—then we are being told very clearly that Solas was actually “corrupted” into a demon thousands and thousands of years ago.