Well first off, we all know that he is the father of the abyss, there really isn't any argument there. However I would like to point out one of the first things about him, his name. This creature is ancient possibly even older than Lordran. One of the things that makes me wonder is the fact that Lordran is obviously just a translation to "Land of the Lords" in some other type of language, could that be the same thing for Manus?
There are two words that we can draw one is Man and the other would just get censored.
This got me thinking on what Manus may in fact be. Let's take in to account that the age of man coincides with the age of dark if we choose the dark lord ending. In other words mankind has something to do with the darkness and possibly the abyss. So is it possible that Manus is also the father of mankind as well?
The other Gods of the world don't exactly like the idea of the age of man coming around so it's possible that they weren't the ones that made mankind, instead it's more likely Manus did.
One of the other things that was mentioned in another topic is that things in the world of Dark Souls, always balance themselves out even if the Gods don't want them too.
So it is possible that there is a cycle that time abides by. (The land of fog (time of dragons), Lordran (time of Gods and Lords), and the age of man, than a reset of it all. Except what happens to the Dark Lord? Does he die like everyone else? Or does something happen to him?
Here's what I'm trying to get at, I think that if the player were to chose the Dark Lord ending what eventually happens to that character is that they turn in to a creature like Manus since they were the ones that started the age of man and possibly fathered mankind.
Why do I think this? Two words, the pendant.
For what we know we are the only ones that have a pendant after the age of dark sets in, and we still bare the memories that the pendant holds with it. It's possible that as the age of man starts to fade away, the character that we played as goes maddens like Gwyn did and turns into Manus and cradles the memories he had when he fathered Mankind.
So why are we able to fight Manus? Blame it on the Oolacilians and one of the primordial serpents for distorting the time in Lordran. I think it began with too much curiosity from both of them that brought Manus into a different time, and he attempted to continue the existence of humanity.
This might also explain the large masses of humanity that are floating around in the abyss, Manus at the end of Mankind's time may have tried warped methods of magic on both man, woman, and children (explaining how they come off in three different shapes)I think the only reason I think this might be the case is because of the description of the pursuers.
"The will feels envy, or perhaps love, and despite the inevitably trite and tragic ending,
the will sees no alternative, and is driven madly toward its target"
The pursuers may in fact be humans that recognize us and move towards our old selves, because they think that we might help them from end their suffering or it could be the other way around that they hate us and they have accepted their fate and only wish to kill us.
So I'd like to know what you think of this theory. Do you think it's plausible or not?