I hate to say it again, but Chris did the major work on the game. I would estimate that although he had seven designers on his team, he did about 50% of the work on the project. Keep in mind that he did all this while he was working on Fallout 2 as well. The man is truly prolific.
For the major character dialogues, I based my work on the original dialogues that Chris had created – some of them were just snippets, but they all held the germs of fascinating ideas - because I felt that the game would be better served to move forward with his vision as the signpost. If I misremember anything I’m about to list, I plead the passage of years and the indulgence of my coworkers.
The areas I did included Smoldering Corpse bar and its attendant quests and dialogues, Many-As-One and the Warrens of Thought, the Great Foundry, some of the Lower Ward (John Deiley did most of the other parts), Lothar and the Bones of the Night (though I don’t remember if I did Mantuok), Many-As-One, Curst, Under Curst (and certain dialogue nodes with Vhailor), Carceri. Trias the Betrayer, and Fhjull Forked-Tongue. I helped smooth out certain kinks in the flow of the game, and suggested some of the chaos that might ensue when Curst shifted into Carceri and helped design the mechanic that would allow the player to return the city to the Outlands. I think I did some other stuff too.
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Chris was almost entirely responsible for the dialogues between the Nameless One and the party NPCs. We could add a few nodes of dialogue here and there, but Chris did almost everything with those characters.