You couldn't find the saint I asked for. Are there different kinds of saints or gurus that the book talks about that might help me understand its perspective?

Yes, the preface of the Shri Sai Satcharita, detailed in Chapter 0, provides a broad and inclusive definition of a Guru that is helpful. While the specific name you're looking for might not be in the text, it states that a Sadguru can be from any caste, religion, or age. It goes even further to say a Guru can be "in person or in the form of a book," and could even be a parent, sibling, or friend. The text also differentiates between worldly Gurus, like great politicians or writers, and spiritual Gurus or saints. The service to the former yields temporary, worldly fruit, while service to the latter yields eternal, spiritual fruit, highlighting the book's primary focus.