Nāgasena was a Brahmin who became a Buddhist sage lived about 150 BCE. His answers to questions about Buddhism posed by Menander I (Pali: Milinda), the Indo-Greek king of northwestern India (now Pakistan), are recorded in the Milinda Pañha.

Sanskrit in origin, Nāga means king cobra, snake, serpent, or dragon, and also can refer to snake-human hybrids, an ancient super-race who were the mythological founders of many Asian countries. Sena means army. Therefore the name can be translated as "Army of Nāga" or "Host of Dragons", signifying a very powerful supernatural presence.

There is almost universal agreement that this text was later expanded by numerous other authors, following the "Question and Answer" pattern established in the early books. The version extant today is very long, and has signs of inconsistent authorship in the later volumes. There is no agreed-upon point at which Nagasena's authorship may be said to end (and the work of other hands begins), nor has this been perceived as an inherently important distinction by monastic scholars.