All of the Corrupted were either part of Elika's family, or part of the royal courtElika becomes especially distraught when fighting the Corrupted, despite the fact that they are clearly evil and need to be killed in order to heal the land. In fact, Elika takes The Prince's habit of taunting the Corrupted quite personally. The most obvious is of course the Concubine, who is Elika's mother (She calls herself the Queen, she is found in the portion of the world that Elika says her mother loved...), The Warrior is probably Elika's grandfather, The Hunter is likely to be her brother, and the Alchemist is probably the court vizier (which is also why Elika doesn't particularly get upset when The Prince beats him). That's why Elika is so bummed when her dad becomes The Mourning King, since it just proves that her family is tainted.
The Prince is OrmazdIt's been discussed on the Just Bugs Me page that the ending of the newest PoP may not be bad, but rather, a nessesary evil, as Ahriman's prison is suggested to be failing due to a lack of regular maintenance and the fact that even if the Prince hadn't broken the seal, someone, someday, would eventually do it again, with Elika long gone to work in stopping him. Thus, the Prince has only done what needs to be done. It's a bit of an inversion of My Death Is Just the Beginning, in that the hero causing the apocalypse is only the beginning, a necessary step to beating Ahriman for good. Who would want to beat back Ahriman for good, quite possibly doing anything necessary to make it happen? His brother and rival god, of course. Elika mentions that Ormazd eventually just up and left...to go ride around on a gold-carrying donkey, perhaps?
The Prince is VerethragnaContrast with the above theory. The Prince isn't Ahura Mazda (Ormazd) but another figure from old Persian mythology: Verethragna (Bahram), the vanquisher, and avatar of Ahura Mazda's glory, who the Greeks associated with Herakles. Verethragna was usually depicted with a large sword - and the Prince has a pretty spiffy one. He was associated with fire and winds - the Prince's outfit and indeed the aesthetic flow of the entire game is reminiscent of this (admittedly that might be stretching things a bit). One of his roles was defending the source of waters from the demons of Angra Mainyu (Ahriman): protecting the fertile grounds? And, on the subject of fertile grounds...
Elika is AnahitaAnahita (Nahid) was the goddess of water, and seen as an innocent and pure figure, and identified by the Greeks as Artemis. As the source and guardian of the waters she was also the source of all life: from water does all life begin. She sustained and fertilized the rivers of the world, and associated particularly with plants and healing; she was depicted as a beautiful maiden wearing golden earrings and embroidery (and also otter furs - it's not a complete match). Elika is presented as a very pure figure (and as the Prince points out repeatedly, she's innocent and very naive); she heals the fertile grounds blighted by Angra Mainyu's corruption, turning the blackened rock into verdant fields.
Ubisoft is setting up a "Rage Against the Heavens" plotThe Prince, based on his dialogue with Elika, is a fundamentally selfish character. Most of his adventuring has been done in order to get rich and live in comfort. Time after time he gets his hands on a fortune, only to lose it. He has no moral objection to looting the dead, since they can't use the treasure and he can. He has no particular use for Ormazd, and doesn't actually believe in Elika's cause. Considering the Prince's selfishness, the only reason he's helping Elika in the first place is so he can get out of the land of Ahura, find his donkey, and continue on his way. However, in the course of his journey with Elika, he comes to care for her. He might even love her, though he does not come out and say it. So, when Elika dies after binding Ahriman, it seems only natural that the Prince might see freeing Ahriman to save Elika as an acceptable trade. After all, Ormazd threw Elika under a bus as soon as he got what he wanted, so why should the Prince care about either of them? As far as the Prince is concerned, Ormazd should fight his own battles and leave humanity out of it.
The Prince Will Become Corrupted in The SequelAs we know, the Corrupted are those who made a pact with Ahirman, which is why they're Cosmic Horrors now. From that, it isn't that much of a stretch to say that the Prince now qualifies, and from what we know of Ahirman, he'll jump at the oppertunity. Note that this doesn't preclude the Prince from being a hero, just a walking reminder of a thoughtless action.
Ahriman is the darkness in Alan Wake.After Ormazd's forces gain enough power, they manage to push him away from the old world and in desperation he withdraws to unknown lands where no one knows of him. Dark stories, which happens to be his true source of power, are not shared in these lands; thus, he grows weak and goes into a deep sleep. The people of the old world reach these lands thousands of years later, and without knowing, a gifted poet among them, a powerful story teller and a follower of darkness like all of his colleagues, tells a story on Ahriman's nest, finally waking him up.
The Prince is already Corrupted by the beginning of the storyIn fact, he is the most powerful of the Corrupted, being even a better combatant than The Warrior, more cunning than The Alchemist, more agile than The Hunter, and his powers of illusion make even The Concubine look pathetic, allowing him to hide his dark presence from even the princess of the Ahuras! The entire game was an Evil Plan to free Ahriman, and it succeeded.
Edit: It just hit me! Doesn't "The Prince" actually sound an awful lot like the name of a Corrupted? It makes even more sense now!
The title of "prince" is literal.The Prince really is royalty. The parents he mentions who died in "someone else's war"? They're a king and queen who were captured and killed by the enemy, while the Prince was sent away for protection. Before he left, the Prince grew up not really caring about anyone else, since he was given all he needed, and he never viewed ordinary people as people. He possibly has an older brother who would inherit the throne instead of him, so he would never need to care about commoners in the first place. Caught up in himself and grieving over his parents, he ran from his responsibilities, and his entire self-focused lifestyle is a result of this. However, a prince running like this wouldn't go unnoticed, so he developed a habit of never revealing his true identity to anyone and stay incognito. He doesn't give his name to Elika not to deliberately be mysterious, but out of habit.