Surely a question that has been on everyone's minds since chapter 628. Robin's simple question surely has more impact on us than it does on her. A lot of people are saying that it has to do with Noah, something about being a shipwright, hiding something else, blabbidy blah, crap like that. Let me be the first to tell you, that theory is for the sea birds. Joy Boy goes back a lot further, and a lot deeper, than just some really huge boat that right now vaguely reminds me of Revelations 1:8.
So back to the question, who were you Joy Boy? To examine this question, let's go back to the root, and by that I mean Japanese root. According to one translation i found, joi can mean investiture. Not knowing anything regarding investitures beyond the world of finance, I then found the following definitions for investiture:
1. The act or process of investing.
2. The formal bestowal, confirmation, or presentation of rank, office, or a possessory or prescriptive right, usually involving the giving of insignia or an official title.
3. the state of being invested, as with a garment, quality, or office.
The last two definitions were what grabbed my attention. Bestowing an official title, and being invested in it. Investment here could just be another word for commitment, but still important. You're probably wondering why I'm giving you a vocabulary lesson. For now, just keep the word "titles" in mind. When Robin read the poneglyph where she first uttered those fateful words, she was reading what she believed was an apology letter. This obviously wasn't anything insignificant, else why preserve it on stone for all eternity? He must have done something pretty bad. But what? Definition 2, the formal bestowal of titles. Let's change his name to Title Boy. He would be responsible for doling out titles to whom ever was supposed to receive them. What if he was responsible for giving a title to someone bad? The Ancient Alliance seemed to be able to take over the Ancient Kingdom with relative ease. This is odd, considering this kingdom would have had the ancient weapons at their disposal.
For a while there has been a theory that the Alliance either originally had the weapons and planted them on the kingdom, or stole them and used them against them. I am going to go with the latter here and apply it to what I have already stated. The question now is how did they get them? Surely something like that would only be accessible by the most trusted of highest authorities. What would you think if I said that the Alliance might not have seen the kingdom as an initial threat? In fact, I would venture so far to say that the Ancient Kingdom was part of the Alliance or the Alliance wanted peace with the Ancient Kingdom. To do that, Joy Boy would have to bestow a title to a representative of the Ancient Kingdom, as an act of goodwill. That person would be a diplomat, and with that, comes diplomatic immunity. That means they could do anything they wanted essentially. They couldn't be arrested but they could easily get their ass deported if it became too much or they did something too severe, so they had to act casual and innocent. Hmm, the power to do anything you want and get away with it... Where have I heard that before? Lethal Weapon 2? Yes, but not what I'm thinking of.
Anyway, of course there couldn't just be one diplomat maintaining all relations between two countries, there would have to be a few of them. And let's not forget the wife and kids. Now we have a whole group of people who can basically do whatever they want in the Ancient Kingdom. And after a while, those people built up a bit of prestige and maybe a little political influnce. Of course, the Ancient Kingdom wouldn't want to be outcasts so they might overlook some things done by diplomats. But what if those diplomats tried something big? Like organizing a coup with help from the outside? They could have seen the kingdom as a threat easily, let's not rule that out. But how could they face an army whose general could not be jailed or killed? Good question.
Let's jump ahead about 99 years. The war is over, and the Alliance is turning into the World Government. Now, credit must be given where credit is due. As thanks, they let the diplomats keep their status and make it a flashier title with a broader domain. Call them the Tenryubito, street name World Nobles. Yes, the Ancient Kingdom would have essentially created the Tenryubito. And how did this all start? How could this have all been avoided? The world would be a different place if Joy Boy never bestowed that title to them. And so, to show his undying regret for his action, he inscribed his apology on stone. Boy makes it even worse, implying he was simply a child. Imagine a child having to bear the fall of a kingdom on his back. Joy Boy's life sounds like it was anything but joyous.