I just had my first battle with Lady Maria...she's the best boss ever. But wait, isn't she the Doll? I'm so confused but also totally in love with her...but fr, did the doll really just fight me?!
I've not played the game myself (can't, no PS), but I've absorbed a fair bit of the lore through the rest of the fanbase.
It was my understanding that the doll was given to him by the Moon Presence. Like, in a disturbing "Oh, you loved this person and want them back? Here, this is the same thing, right?" sort of way.