There aren't any characters per se in Leo Strauss' book, Natural Right and History. It's a work of non-fiction, so characters don't appear in it in the same way they appear in a novel. However, if you consider characters as actors or influences, then the scope for discussion is very great, indeed. That's because Natural Right and History is about whether there is justice inherent in Nature, and whether that confers "natural rights" on us. In other words, humans have rights that can't be taken away by any government, because they're part of Nature. That's not to say they're part of human nature. Natural rights are much bigger than that. They're part of Nature with a capital N. This is a contentious, much-debated topic among professional historians and philosophers. Strauss is considered by most of us to take a more conservative or right-leaning view of these questions, as opposed to the more liberal or left-leaning view taken by Karl Marx or Gary Chartier.

People make history. It doesn't just happen. That's why the scope for discussing "characters" in Leo Strauss' book is great. Individuals can influence history. So can groups of people. So can institutions created by people, like governments. Some of these characters are more influential than others, by virtue of their power or notoriety or the consequences of their actions. Strauss considers the ancient Greek philosophers so important that he elevates their ideas above all others in his book. He explicitly judges them more valuable than nineteenth and twentieth century philosophers, especially left-leaning ones, who he criticizes in the text for "relativism," or the notion that there aren't any absolute principles, like natural rights, and that history is only a sum of the forces created by the people who live it.