Yaksha (yakṣa)

Yakshas are nature spirits attached to trees, lakes and hidden treasure, attendants of Kubera the lord of wealth, and generally guardians rather than aggressors. The Mahabharata's most famous yaksha guards a forest lake, strikes down four Pandavas who drink without answering him, and puts a long series of riddles to Yudhishthira about the nature of the world and of duty. He turns out to be Yama, and the answer that wins his brothers back is a piece of ethics rather than cleverness.