According to Official Guinness Records,
The largest single volume biography was written by Dr. A.V.S. Raju (India). It was written between 1996 and 2007 and chronicles the life of Sri sathya Sai Baba (India). The single bound book consists of 32 separate volumes.
Dr. A.V.S. Raju says he will continue writing and adding to the biography.
For a complete list of 2007 records, please visit 2007 Guinness Records in India.