My first instinct thought was "Avatar". I think the original and common meaning is more like a manifestation/aspect or emanation of the deity itself, not another creature chosen by the deity. However I like messing things up a bit and create confusion on anything related to religions in a RPG, and calling saints "avatars" can in fact increase the ambiguity... are they really separate creatures after all? Have they ever been separate from the deity they now serve, or were their mortal lives a decoy? Anything driving inquisitive players nuts is lovely.
After reading the OP, I also had a conversation with a couple of generative AIs on this topic, and they both approved the choice, which makes it even more disturbing...