You remember Hubert, right? He's the guy who's assigned the unpleasant task of burning out little Arthur's eyes with a hot poker.
Before we go into detail about Hubert's character, we have to clear up one possible source of confusion. In the original printing of the play, Hubert makes his first appearance at line 325 of Act 2, Scene 1, making him the second citizen of Angers to address King John and King Philip. But most modern editors argue that the First Citizen who appears on the walls at line 200 of that scene is actually the same character. (Shakespeare can be a little sloppy with names at times.)
So, depending on what edition of the play you're reading, some of Hubert's lines may be given to another character. What difference does it make? Not a big one, really. The main effect of giving all these lines to Hubert is that it really makes it seem like he doesn't start out being loyal to John. Instead, thinking about what's good for his city, he insists on holding out until one of the kings has triumphed in battle.
If you think about it, this is a pretty sensible course of action. What's the point of supporting one king, only to have the other king besiege your city, level it to the ground, and then kill you for supporting the other guy? Figuring out in advance who is stronger is a much smarter course of action—though it doesn't sit well with traditional notions of loyalty.
Strangely enough, though, once fighting erupts for a second time between King John and King Philip (after the wedding of Blanche and Louis), Hubert is squarely on the side of King John. Does this reflect the fact that Shakespeare hadn't fully thought the character out? Or is he supporting John because he thinks it's in the best interests of Angers, just as earlier he didn't support him, because he didn't think it was in Angers's interest?
The play doesn't give us an answer. In any case, once the battle is over, Hubert has suddenly morphed into one of King John's most trusted advisors, the one he gives the unpleasant job of murdering young Arthur to. But why is Hubert so ready to head to England and do King John's dirty work? Won't that take him away from Angers, where he's a prominent citizen? Who would give up being mayor or city counselor or some such position in order to become a sneaky murderer?
This doesn't seem to make much sense—though doesn't it seem to parallel the Bastard's decision to abandon his claim to the land of Robert Falconbridge, Sr. in order to become known as the son of Richard the Lionheart (and to become King John's henchman)? In any case, like the Bastard, Hubert remains one of the king's loyal servants for the rest of the play, and he sticks with John even though the English lords turn against him and ally themselves with France.
But Hubert's biggest scene in the play doesn't involve being loyal to King John; it involves his disloyalty. This, of course, is the scene in the castle, where he is supposed to put out Arthur's eyes with hot pokers and presumably murder him… but can't bring himself to do it. As we learn from the dialogue in this scene, Hubert and Arthur have bonded during the time that Arthur has been held prisoner. Apparently, Arthur has even nursed Hubert through an illness.
So it was bound to be difficult for Hubert to go through with the deed. In a sense, you could say that Hubert sets himself up to fail when he sends the other executioners out of the room. Don't you think he must have known that once he found himself alone with the child, he would be unable to do it? Do you think setting himself up to fail in this way was a conscious decision on his part, or unconscious?
Another question: if Hubert knew all along that he was supposed to kill Arthur, why did he let himself bond with him in the first place? Shouldn't he have had total control over the situation? If Hubert shows us anything, maybe he shows us how complicated it can be to navigate through these dangerous political waters and make it through in one piece.