Nāgasena is the central figure of the "Milindapañha" (Questions of King Milinda), a dialogue with the Greco-Bactrian king Menander that uses the famous chariot simile to explain the Buddhist doctrine of non-self (anattā) - just as "chariot" is merely a conventional name for an assembly of parts with no separate chariot-essence apart from them, "person" is a conventional label for the five aggregates (skandhas) with no separate, persisting self behind them.
Intellectual setting
The "Milindapañha" reflects the philosophical and cultural encounter between Buddhist thought and the Hellenistic Indo-Greek kingdoms of northwest India, with Menander I a historically attested ruler whose engagement with Buddhism is corroborated by other sources.
Key ideas
The chariot simile
Nāgasena argued that just as none of a chariot's individual parts, nor their mere collection, constitutes a separately existing "chariot" beyond a conventional label, a person is likewise a conventional designation for the five aggregates rather than a separately existing self.
Dialectical defense of non-self to a skeptical interlocutor
Through sustained question-and-answer with King Milinda, Nāgasena modeled a method of reasoned philosophical dialogue used to clarify and defend the Buddhist metaphysics of personal identity against an skeptical outsider's objections.
Legacy
The "Milindapañha" became one of the most important para-canonical Buddhist texts, especially influential in Theravāda Buddhism, and Nāgasena's chariot simile remains one of the most widely cited arguments in comparative philosophy of personal identity.