In chapter 4 of Freak the Mighty, Kevin and Max are getting to know each other, and they are talking about all kinds of things. At one point in the conversation, Max asks why Kevin calls his mom "Fair Gwen of Air." Kevin explains that he has nicknamed his mother after Guinevere from the legend of King Arthur. Max tries to act like he knows what that is, but Kevin is a smart kid and a quick study of people. He goes on to better explain who Guinevere and King Arthur were.
What's most important about the legendary king isn't that he may or may not have existed. Kevin doesn't care. What Kevin cares about is the imaginative inspiration that King Arthur, his knights, and his kingdom are to him. Kevin explains how Arthur came to power. He explains a little bit about the Round Table, and he explains how Arthur would send his knights on special secret missions called quests. Kevin loves the idea of quests and going on quests to save fair damsels in distress. It's one of the reasons why he wants to return the purse. Kevin is extremely passionate about all of it, and it's clear that he sees much of himself in King Arthur, as he refers to the hero as a "wimpy little kid" who ended up doing things no others could. Kevin's imagination is as large as it is infectious, and Max can't help but be pulled along into these fantastic "quests" that Kevin comes up with. When Max is with Kevin, they are the stuff of legends, just like King Arthur. Together, they are Freak the Mighty.