Uddalaka Aruni (fl. c. 8th century BCE), (Devanagari: उद्दालक आरुणि) also referred to as Uddalaka or Aruni or Uddalaka Varuni, is a revered Vedic sage of Hinduism. He is mentioned in many Vedic era Sanskrit texts, and his philosophical teachings are among the center piece in the Brihadaranyaka Upanishad and Chandogya Upanishad, two of the oldest Upanishadic scriptures. A famed Vedic teacher, Aruni lived a few centuries before the Buddha, and attracted students from far regions of the Indian subcontinent; some of his students such as Yajnavalkya are also highly revered in the Hindu traditions. Both Aruni and Yajnavalkya are among the most frequently mentioned Upanishadic teachers in Hinduism. According to Ben-Ami Scharfstein, a professor emeritus of Philosophy at Tel Aviv University, Uddalaka Aruni was one of the first philosophers in recorded history. Debiprasad Chattopadhyaya established Uddalaka Aruni as the first ‘natural scientist’ in the intellectual history of the world. In the Chandogya Upanishad, Aruni asks metaphysical questions concerning the nature of reality and truth, observes constant change, and asks if there is something eternal and unchanging. From these questions, embedded in a dialogue with his son, he presents the concept of Ātman (soul, Self) and Brahman (universal Self). Source: Wikipedia (en)