Atma Vidya was written by Sri Ramana Maharshi. Muruganar was instrumental in the creation of this book.
Muruganar wanted to recast a popular Tamil poem that begins, “Lo, very difficult is Self-Knowledge.” This did not express what Ramana taught and experienced directly, and Muruganar wanted Ramana's version. Muruganar started: "Lo, very easy is Self-Knowledge, Lo, very easy indeed." He asked Ramana to finish it. Bhagavan’s response was to write these five verses called Atma Vidya or “Self Knowledge.”
Here's the first verse
Lo, very easy is Self-Knowledge, Lo, very easy indeed. Even for the most infirm So real is the Self That compared with it the amlak In one's hand appears a mere illusion.