Short answers, pulled from the story.
Nagarjuna was a philosopher and Mahayana Buddhist monk from South India, conventionally dated to around 150-250 CE. He is widely considered the most important Buddhist philosopher after the Buddha himself, and in Tibetan Buddhism he is called the "second Buddha." He founded the Madhyamaka school and his writings on emptiness shaped Mahayana Buddhism across India, China, Tibet, Korea, and Japan.
The Mulamadhyamakakarika, or Root Verses on the Middle Way, is Nagarjuna's best-known work and the foundational text of Madhyamaka philosophy. It is composed of concise aphoristic Sanskrit verses that argue all things are empty of inherent, independent existence (svabhava) by systematically refuting substantialist theories across topics including causation, time, movement, personal identity, and nirvana. The text has been translated into Chinese, Tibetan, Korean, and Japanese and continues to be studied today.
For Nagarjuna, emptiness means that all phenomena lack svabhava - inherent, independent existence. Nothing arises by its own power; everything depends on causes, conditions, and conceptual frameworks. Emptiness is not nihilism but an explanation of dependent arising: all things exist only relationally, and recognizing this is the basis for liberation from suffering.
Nagarjuna articulates the two truths doctrine in chapter 24 of the Mulamadhyamakakarika: conventional truth refers to ordinary discourse and shared practices, while ultimate truth refers to emptiness. He argues that without conventional truth as a basis, the ultimate truth cannot be taught, and without understanding the distinction between the two, one cannot understand the Buddha's teaching or attain nirvana.
The Chinese Canon includes over 22 texts attributed to Nagarjuna, while the Tibetan Tanjur contains over 140. Scholars disagree on which are genuine. Jan Westerhoff relies on six works he considers most reliably authentic: the Mulamadhyamaka-karika, Vigrahavyavartani, Sunyatasaptati, Vaidalyaprakarana, Yuktisastika, and Ratnavali. Christian Lindtner accepts a larger list but other scholars have challenged several of those attributions.
Several contemporary analytical philosophers including Graham Priest, Jay L. Garfield, Mark Siderits, and Jan Westerhoff have drawn on Nagarjuna's work in their own writings. Westerhoff's The Non-Existence of the Real World (2020) engages directly with Nagarjunian anti-foundationalism, and Priest's Beyond the Limits of Thought (2002) includes a chapter on Nagarjuna. The Italian theoretical physicist Carlo Rovelli credits Nagarjuna as an influence on his relational interpretation of quantum mechanics in his book Helgoland.