Like Thomas More, Peter Giles is also a real, historical figure. Unlike Thomas More, very few people have heard of him. In fact, if he's known at all, it's for being Thomas More's friend in Utopia.
All we really get about this guy are the absolute basics. He's Dutch, smart, and an all-around solid guy. You can't get much higher praise than this: "apart from being cultured, virtuous and courteous to all, with his intimates he is so open, trustworthy, loyal, and affectionate that it would be hard to find another friend like him anywhere" (1.9). Aww... tear.
But, why do we care? Although it's true that Giles's and More's friendship is a pretty minor aspect of this book, it points to the importance of having these kinds of strong, interpersonal connections in a world where global travel and new world discovery is becoming more and more common.
The friendship is also a subtle example of how Hythloday's doom-and-gloom portrait of modern Europe isn't totally fair. Even though many of the problems of Europe he describes are horrendous, and even though Utopia offers a powerful model of a peaceful community, community is still a part of Europe. People are still friendly and form trustworthy, life-long friendships. In fact, do we remember Hythloday mentioning anything about friendship in Utopia?