What are the primary Guru biographies discussed in the preface, and who wrote them?

The preface highlights two main, detailed Guru biographies. As noted in Chapter 0, the first is the 'Brihat Guru Charitra' by Shri Saraswati Gangadhar, a well-known work studied daily. The second is the 'Shri Sai Satcharita' by the late devotee Shri Govind Raghunath alias Annasaheb Dabholkar, which is a biography of Sai Baba. The text explicitly states that apart from these two, no third work written in such detail is readily found. It does, however, also mention two much shorter biographies of Baba written by Shri Dasganu Maharaj.