Aruni Uddalaka
Aruni or Uddalaka or Uddalaka Aruni (fl. c. 7th century BCE) was a philosopher of Vedic India, whose teachings are recorded in the Brihadaranyaka and Chandogya Upanishads. One of the first philosophers inrecorded history, he taught that everything in the universe (including all living things) is made of three elements: heat (or light), water, and food (or plants), and furthermore that all of these were manifestations of the universal Self or Ātman. It has been suggested that his teachings contain the seeds of Indian atomism, because of his belief that "particles too small to be seen mass together into the substances and objects of experience".
A descendant of Varuni Bhrigu clan, Uddalak rishi had his Ashram in the Vedic state of Brahmavarta where Ashrams of other Vedic seers Piplada, Dadhichi, Chavan also existed. These Rishis are the composers of the oldest of 10 Upanishads which date back to Rigved period. They also have contributions to Vedas. Aruni hailed from the country of Panchala and was known as Aruni of Panchala. His son wasSvetaketu.
Aruni was one among the disciples of sage Ayodha Dhaumya, along with Upamanyu and another named 'Veda' (Mbh 1.3). As per Mahabharata (MBh 1.3), on one rainy night Aruni's preceptor Dhaumya Muni asked him to supervise water flowing through a certain field. Aruni went there and found that water had breached the field and was moving away from its designated path. Aruni tried to stop water by all means but was unsuccessful. Left with no other way, Aruni lay down on the breach and prevented the water flow using his body. Due to this Aruni did not return to the hermitage in the night. Later in the morning, Dhaumya Muni came to the spot in search of Aruni with other disciples. Upon seeing the dedication and sincerity of Aruni, Dhaumya was very pleased upon Aruni and gave him the title Uddalaka. Later Aruni became very famous under the name Uddalaka Aruni.
In the Katha Upanishad, Uddalaka Aruni has been portrayed as a very learned sage who had performed numerous yajnas. Uddalaka Aruni was also called Vajashravas because he organised innumerable community feeding programmes. Vajashraavas had one negative quality as he had no control over his anger and flew into uncontrollable rage at trifles. His wife was Vishwavaradevi. The son of Vajashravas was the great young seeker Nachiketa. In a feat of rage Vajashravas had given Nachiketa to Yama, the death.
Uddalaka Aruni is said to have systematized the Vedic and Upanishadic thoughts. Many Sutras are ascribed to sage Uddalaka Aruni. Among those, "Tat Tvam Asi" illumines the Chāndogya Upanishad, which is a part of the Sama Veda. This great utterance is repeated nine times in this Upanishad as the ultimate Truth, which reveals itself as the conclusion of each inner experiment. The teacher is Uddalaka and the student Svetaketu, his son, engaged in a profound soul-education.