I've been working on a project that requires multiple AI "characters" to behave differently in the same conversation — think of it like NPCs in a game, except each one needs to respond based on their role, personality, and the current situation.

Here's what I learned about making this work reliably.

The problem

If you just tell an AI "you are character A" and "you are character B" in separate prompts, they all end up sounding the same. Generic. Helpful. Boring. You need them to have distinct behaviors — one should be cooperative, another defensive, another authoritative.

What actually works

1. Behavioral constraints > personality descriptions

Bad:

You are a friendly witness who is helpful.

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Better:

You are a witness being questioned.…