what is nameless one?

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i have finished planescape torment a couple of time but i have many question about name less one. i know nameless one level up to the more then 46 and i think he can go to the 99 level.in reality his all stats are 25 and 25 is the highest stat in the 2. edtition .it seems nameless one is powerful than demigods even gods in the multiverse.but can we learn what he really is? because end of the game namless one go to the blood war for his punishment . what was his sin and who can punish this guy?