Wikipedia
The Keśin were long-haired ascetic wanderers with mystical powers described in the Keśin Hymn (RV 10, 136) of the Rigveda (an ancient Indian sacred collection of Vedic Sanskrit hymns). The Keśin ("long-haired one") are described as homeless, traveling with the wind, clad only in dust or yellow tatters, and being equally at home in the physical and the spiritual worlds. They are on friendly terms with the natural elements, the gods, enlightened beings, wild beasts, and all people. The Keśin Hymn also relates that the Keśin drink from the same magic cup as Rudra, which is poisonous to mortals.
The Kesin hymn of the Rigveda is the earliest evidence of yogis and their spiritual tradition, states Karel Werner. The Hindu scripture Rigveda uses words of admiration for Kesins.