Malthael, Archangel of Wisdom - Archangel of Death
Okay so everyone who follows the story has probably already found out that Malthael has abandoned his post as the Archangel of Wisdom because he was unable to comprehend the destruction of the worldstone. Tyrael suggests that he is wondering Pandemonium in search of answers to the things that plague him.
To me, I am kind of thinking that Malthael is the Prophet that the enchantress talks about. My reasoning behind this belief is that going through the Enchantress' story throughout the game, you eventually learn that her master, The Prophet, was actually an angel. She says that the letter from the dying angel saw promise in humanity, and worked in absolute secrecy. Itherael was unable to look into his scroll and see his fate, and so he knew nothing of him.
If Malthael was the Archangel of Death, then that means he would have to ability to phase in and out of different times in history, just like how the enchantress was sent into the future. Also, maybe it is possible Itherael was unable to find out who the Prophet was because Death is itself, and thus has no predetermined fate to head towards, and Itherael was always so aloof, being drowned in the Fate of everything that he never really noticed anything.
Perhaps Malthael went back in time before the worldstone was destroyed in an attempt to restore the balance he felt was disrupted when the Worldstone was destroyed, and trained a group of young magically gifted young girls who showed potential in slaying demons to go into the future, when balance is completely out of order and in the favor of Hell, to help the hero restore what he feels is missing since the destruction of the Worldstone. That's just my theory on Malthael anyways.
Covetous Shen -
Everyone knows going through Covetous Shen's story that the main character is almost entirely convinced that he actually is a God like people believed him to be. Some people feel that Covetous Shen is actually an Archangel, some even go so far as saying he is actually Malthael in disguise. I have my own theory however on Covetous Shen's true identity, although you guys might find it bit of a stretch.
I think Covetous Shen is actually the Demon God of Greed. I think all the Treasure Goblins found throughout the game work for Covetous Shen, helping him to search for that mysterious gem he has been looking for, for so long.
I say he is the demon lord of greed and I know quite a few will find it farfetched but it has been made clear that not all demons and angels are "for the cause" so to speak. If there is a Lord of Greed, then he would be in love with shiny, precious objects, like gems, and he would covet them accordingly.
Perhaps this is why he is not worried about wondering through places infested with demons? His attitude and personality seem to point towards this end, for me at least. Also, his dialog with his guide, Gaven when you first rescue him and find the object he is looking for seems like he could care less about life, as long as he obtains items.
This is all just my two cents at least. Let me know what you guys think.
Archangel of Wisdom/Death Malthael I belive is the Prophet from the Enchantress story.
I believe Covetous Shen to be the Demon Lord of Greed.