Concept:The title "al-Hafiz" refers to a person who memorizes the Qur'an completely.Explanation:Ali ibn Abi Talib was given the nickname al-Hafiz because of his deep knowledge and complete memorization of the Qur'an.He was among the early Companions who learned the entire Qur'an directly from the Prophet Muhammad.Thus, the nickname highlights his role as a guardian and memorizer of the Qur'an, not his deputizing for the Prophet, writing hadith, or fighting in battles.Answer:Therefore, Ali was nicknamed al-Hafiz because he memorized the Qur'an. (Option C)