http://dragonage.wikia.com/wiki/Keeper
Yeah, I think it was in Inquisition that we got confirmation that Keepers are the remnants of the Dales' priesthood.
And spent most of their time gathering old elven lore and accumulating it. So we can thank them to the trippy laser defense forts in the Dales. 
Gisharel is, according to the Wiki, attributed with writing:
Fen'harel, the Dread Wolf
Vallaslin: Blood Writing
Ghilan'nain, Mother of the Halla
Falon'din, Friend of the Dead, the Guide
Elgar'nan, God of Vengeance
Arlathan: Part One
Arlathan: Part Two (The Sequel)
Sylvaise: The Hearthkeeper
All of which are the things we've found to be spectacularly wrong. Hmm. 
I can't help but wonder if he was one of the Keepers back when that meant Keeping a Temple rather than leading a tribe, and that he was one of the first to lead a tribe after the Dales fell. So he managed to hide away whatever secrets his fellows had found, and remake his people's history as he saw fit. A terrifying amount of power.
And possibly an academic crime that puts Loghain's coup and Howe's Howeness to shame! (Okay, okay, so maybe not from the perspective of everyone that's not me.
)
(I'm still real curious about the Dales' system of governing. Was it a kingdom? A tribal council? A magocracy? I'm guessing some kind of veneration of elders was involved.)