Because Guns, Germs, and Steel is a work of nonfiction, it does not have characters in the same sense a novel would. In a way, Diamond, having done all the research and made all the arguments in the book, is it's main character. But in a powerful sense, the main "character" of the book is a man named Yali. Diamond describes Yali as a "remarkable local politician" who lived in Papua, New Guinea. One day, while Diamond was on a research trip to that island, Yali asked him a question:

Why is it you white people developed so much cargo [i.e., material things] and brought it to New Guinea, but we black people had so little cargo of our own?

Diamond writes that Yali's question gets at one of the most vexing problems facing students of human history. Why is it that some peoples, particularly Europeans, developed the technology necessary to dominate other peoples around the world? Why didn't it work the other way around? Diamond frames the entire book as his answer to Yali's question. He argues that people like Yali lived in regions where, entirely due to geographic accident, the trappings of large, settled, agricultural societies—the "guns, germs, and steel" that allowed Europeans to dominate the rest of the world for centuries—developed relatively slowly or not at all. Yali's people did not fail to develop "cargo" because of something lacking in their culture or their genetic makeup, but because geography militated against it. Thus, Diamond's book is an answer to Yali's question and a firm statement against racist theories of human development that marginalized people like Yali. For these reasons, Yali can be seen as the main "character" of the book.