Final answer:
James Randi, a retired magician and skeptic, offered a million dollar reward through the James Randi Educational Foundation for proof of dowsing or psychic abilities, a challenge which remained unclaimed until it was terminated in 2015.
Step-by-step explanation:
The individual who has offered a million dollar reward for anyone who can demonstrate that dowsing or other psychic powers are genuine is James Randi, a Canadian-American retired stage magician and a scientific skeptic. He is well-known for his challenges to paranormal claims and pseudoscience. The James Randi Educational Foundation (JREF) had historically offered a prize of one million dollars to eligible applicants who could demonstrate a supernatural or paranormal ability under agreed-upon scientific testing criteria. The prize was terminated in 2015 after over 50 years of the challenge being unclaimed, which supporters of Randi's challenge point to as evidence of the non-existence of such powers.