Aruni

Aruni (c. 8th century BCE), also referred to as Uddalaka or Uddalaka Aruni, 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 few centuries before the Buddha, attracted students from far regions of the Indian subcontinent, some of his students such as Yajnavalkya are also highly revered for their ideas 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. Aruni asks metaphysical questions, the nature of reality and truth, observes constant change and enquires if there is something that is eternal and unchanging. From these questions, embedded in a dialogue with his son, he presents the concept of Ātman (soul, Self) and universal Self.

The name Aruni appears in many of the Principal Upanishads, in numerous verses. For example:

Sage Aruni is revered in the Hindu tradition, and like many of its revered ancient scholars, later era scholars from the earliest times attributed or named their texts after him. Some of these treatises include:

Uddalaka Aruni is said to have systematised the Vedic and Upanishadic thoughts. Many Mahavakyas are ascribed to sage Uddalaka Aruni. Among those, "Tat Tvam Asi" (That thou art) of the Chandogya Upanishad is an oft quoted thought in Hinduism. Its teacher is Uddalaka Aruni and the student his son Svetaketu.

...
Wikipedia