The correct answer is: Buddhaghosha.
Buddhaghosha was a 5th-century Indian Buddhist monk, scholar, and commentator. He is considered to be the greatest commentator of the Buddhist canonical literature. He wrote commentaries on the Pali Canon, the Agamas, and the Mahayana sutras. His commentaries are considered to be authoritative and are still studied by Buddhists today.
Nagarjuna was a 2nd-century Indian Buddhist philosopher and founder of the Madhyamaka school. He is considered to be one of the most important figures in Mahayana Buddhism. His works are still studied by Buddhists today.
Ashvaghosha was a 1st-century Indian Buddhist poet and philosopher. He is considered to be the author of the Buddhacarita, a biography of the Buddha, and the Saundarananda, a poem about the conversion of the Buddha’s cousin Nanda.
Vasumitra was a 3rd-century Indian Buddhist scholar. He is considered to be the author of the Abhidharmakosa, a compendium of Abhidharma teachings.
All of these figures were important in the development of Buddhism, but Buddhaghosha is considered to be the greatest Buddhist commentator of the Buddhist canonical literature.