Atreya (आत्रेय) Rishi, or Atreya Punarvasu, was a descendant of Atri, one of the great Hindu sages ( rishis) whose accomplishments are detailed in the Puranas. Sage Atreya was a renowned scholar of Ayurveda and six schools of early Ayurveda was founded based on his teachings. He is credited as the writer of Bhela Samhita, dating to a period of 6th century BCE. He is believed to have worked as the personal physician of King Nagnajit of Gandhara Kingdom, who finds mention in the Mahabharata. The original contents of Charakasamhita are credited to Atreya, which were in turn codified and edited by Agnivesha and Charaka. According to Surendranath Dasgupta, The old Ayurveda of Atreya-Charaka school probably has its root in the now extinct Caranavaidya branch of Atharvaveda.