Reimian Empire

So, to understand the player's character, does the GM need to go out of their way and send various NPCs to interact with them, painstakingly extracting their history and personality?

Well, if he considers this important information for himself, then yes. But if neither the GM nor the players are interested in it, what's the point of writing all this?

I committed murder only once, when the character was already a walking corpse.

Ah, well, if it was only once, then it doesn't really count. One time doesn't make you a homosexual, as they say.