40k is known for its expansive universe and the ease with which one can create and fit their own dudes/storylines within the already-established canon. The producers could pull a Legends of Andor and just focus on telling a killer sci-fi story with the world already built for them.
There's a few voices out there asking to have him play Eisenhorn, who is an Inquisitor, which would open up detective based storylines into heresay/ corruption/whatever. Can go any direction really with him starting out doing regular loyalist inquisitor stuff and slowly discovering just how bad the imperium is.
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