Thanks guys.
I just discovered the Ward, Captain and Commander achievements existed... for some reason, even though I don't have those, it didn't show up for me as ones I didn't have on the personal achievements steam page.
This is a good game, but I don't think I'll bother playing it again on the harder difficulties just to get 100% achievements... especially since there only seems to be one main ending (Unless you count the one where you abandon Avernum and stay on the surface lol). I'll go and kill the emperor now.