I am continuing my speculation on the fantastic series, the Kingkiller Chronicles. I've discussed Denna, the identity of Master Ash, the use of Copper, and what the plan of the Chandrian might be.
In this post, I want to look at the title "Kingkiller", and the name "Poet-killer" given to the sword Caesura.
Obviously, Kvothe is called Kingkiller because he kills at least one king.
Most people have offered that Ambrose is that king. He has, after all, been steadily rising in the ranks to the throne of Vint. His father's barony is known as the "pirate isles", and piracy seems to have eliminated an entire family before him in the ascendency, along with a few stray assassinations here and there. By the end of the third book, Ambrose will have become king of Vint, will pick some childish and petty fight with Kvothe (why a king would do that I can't fathom), and Kvothe will kill him, leaving the entire Four Corners of Civilization in to endless war as the Penitent King takes over.
Some have proposed that the Maer is the Penitent King, most notably because the Penitent King's soldiers wear the same colors as the Maer's house, and also the description of the Maer as angelic after recovering from a night of lead poisoning. However, the Maer is further in the ascendency than Ambrose (as is Meluan Lackless), so the Maer being the Penitent King directly contradicts Ambrose being the king that Kvothe will kill.
Some have suggested that the king Kvothe kills is the one right before Ambrose; that Kvothe has some Amry-ish "greater good" reason to kill this king, but that ironically it leads instead to the snot-nosed brat Ambrose taking over the throne of Vint and going on to conquer the world. It explains the focus on the tension between the two, it explains Kvothe's constant narrational regrets of his foolishness after describing a brilliant victory over Ambrose, and it explains why Kvothe felt so guilty after his actions that he ran out to some no where town to be an innkeeper instead.
Whatever the case, Ambrose still has a very important role to play in the future. We know this because anytime Ambrose is mentioned, Kvothe reflects on what a fool he was to think him harmless. There is some great, terrible, destructive thing that will come about due to Ambrose, whatever it is.
I think it very likely that the Maer is the Penitent King. For instance, when the Maer rebukes Kvothe for wearing a sword in his presence, Kvothe says that the people in the king's court do so. The Maer says that the king will soon pay the price of this negligence; which seems a subtle hint at an assassination plot. The Maer might be trying to take back the kingdom that would be his "but by a fluke in history". He expresses enough resentment at the king. He specifically chooses a bride who is not influenced by the king, maybe so he won't have to worry about loyalist inlaws. He has the motivation and the means, and it seems that subtly he is making the machinations of doing so.
More than anything, though, the soldiers of the Penitent King are wearing the Maer's colors. They may be the colors of the brigade they happen to be part of, or some other noble's colors, or colors assumed by the Penitent King in tribute to the Maer, but the Maer himself seems the most likely candidate.
We know, apart from the king and the angel, that Kvothe is to kill at least one poet, earning Caesura the name "poet-killer". Some have combined the poet and king together, claiming it is the poet king that Veshaya used to work for. This has been dismissed, as he is a small king in the small kingdoms, a region that has barely even been mentioned except to note how terrible its roads are. The death of such a small and insignificant leader seems unlikely to spark a war that ruins most of civilization. Kvothe might actually kill this man (after all, why mention him in the first place if he never comes up again), but I don't think it's the king that earns him the title of Kingkiller and sends him in to hiding in Newarre.
That said, I could make an argument that the state of the world isn't about the death of the king per se. The Penitent King purposely chooses (or is given) a name with religious connotations, and Kvothe has gotten mixed up with demons and angels. He apparently does something to open a door to the Fae, allowing creatures like skrael and skin-dancers to wander in the waking world. Perhaps it is the death of the angel (in Imre's town square) that really sparked the rise of the Penitent King? How would you expect people to react to the death of a literal angel and some earth-shattering event that has monstrous spiders made of stone with razors for feet storming from dimensional portals and killing whole towns? They would rally around some sort of religious leader, either in the sense of a leader of religion or a leader who is religious, seek out the wicked person who slew one of Tehlu's angels, and otherwise try to unify around expelling the Faen invaders. All of the Tehlin countries might join in, seemingly overnight - both the Commonwealth and Modeg seem to be largely governed by the people, Aturas seems to be a theocracy, and the superstitious Vints might sweep all the power out from under their own kings and pledge loyalty to the Penitent King. That Kvothe killed a king is something he may have done in his search for vengeance that forced him to take unsavory pathways, but not necessarily be what destroys everything around him. I have no idea who this Penitent King might be, but really my point is that in the wake of the events we know are going to happen (show downs with the Chandrian, battles with angels, doors to fairy realms being opened and "demons" pouring out in to the mortal world), the entire world is going to be extremely unstable and things like who is in what order to the throne will not necessarily be important.
There are other poets in the story. Ambrose is a poet, and the poet-king is (obviously) a poet. Denna has a friend named Gregory who is a poet, who comes upon bad luck and makes poor decisions with money; for instance, Denna has had to sell her emerald earrings to Devi to make up for a loan Gregory took out. There is also Simmon, Kvothe's best friend. Any number of these might be the poet(s) that is (are) killed. However, I think Sim is specially slated to die in the next book. You will notice, in the story, that Sim is treated with a special amount of nostalgia and attention. Much more than Wil, he is spoken of kindly by Kvothe. If Kvothe ends up, for some reason, having to kill Sim, that might account for a lot of the way Sim is treated in the story, but also the toast Kvothe gives to good friends who "deserve better than they got", the way he looks at Aaron when he calls Caesura the "poet-killer", and why the story of the sword being a "poet-killer" spread -- killing a king and an angel is pretty huge; killing a poet not so much. Any of these are possibilities, but I think it very nearly certain that Kvothe, for reasons unknown, will have to kill his closest and kindest friend, Sim.
Whoever ends up being the killed-king, I do not think it likely that Kvothe has neglected to mention him yet. We have heard a lot of build up in the fight with Kvothe and Ambrose, and also a lot of insight in to the character of the Maer. Even if we can't say for sure which of these is what, or that any of them is anything, I do think it is safe to say that they both have much larger roles to play in the upcoming book. If a candidate is to be found for Penitent King and killed-king from the known cast, these are certainly the most likely options.