Raikva

Raikva, the poor unknown cart-driver, appears in Chapter IV of the Chandogya Upanishad of Muktika canon where it is learnt that he knew That which was knowable and needed to be known, he knew That from which all this had originated. Along with Uddalaka, Prachinshala, Budila, Sarkarakshaya and Indradyumna, who respectively held earth, heaven, water, space and air to be the substrata of all things, and many others, Raikva was one of the leading Cosmological and Psychological philosophers of the Upanishads. He imparted the Samvarga Vidya to King Janasruti. Like Indradyumna he too held air to be substratum of all things.
King Janasruti, the ruler of Mahavrisha, was famous for his philanthropy and charity who was proud of what he gave away as gifts and in charity. He had come to know about Raikva by chance from the swans, who already impressed by his deeds of charity, had seen him, and whose conversation he happened to overhear.