The Katha Upanishad tells of the boy Nachiketa, who comes to the house of Yama and asks what remains when a person dies. Yama offers him wealth and long years in place of an answer, and Nachiketa sets them aside. The dialogue that follows gives the image of the Self as the rider, the body as the chariot, the intellect as its charioteer, the mind as the reins, and the senses as the horses.
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The Katha Upanishad is a conversation between a boy and Death. Nachiketa, sent to Yama's house by his father's careless word, refuses every gift except the answer.
Source: Katha Upanishad 1.1–1.3