Ruhollah Khomeini held the religious title of Ayatollah, which is a high-ranking title given to Twelver Shi'a clerics. He was also a marja' ("source of emulation"), a Mujtahid or faqīh (an expert in Sharia), and the author of more than 40 books.
Ruhollah Khomeini Knowledge Quest: 21 Questions for the intellectually curious