Exegesis (Tafsir) of the Qur'an
The principal exponent of the exegesis (explanation or critical interpretation of a text) of the Quran was Abdullah ibn Abbas ibn Abdul Muttalib. He was the cousin of the last Prophet and Ali ibn Abi Talib.
Reynold A. Nicholson says in his book, A Literary History of the Arabs: "The real founder of Koranic Exegesis was “Abdullah b. Abbas”. Abdullah ibn Abbas was a pupil of Ali ibn Abi Talib and learned all the sciences of Quran from him.