James Randi used to be a magician and went by the name of The Amazing Randi. He was a “trickster”. Later on, however, he devoted his life to demystifying those who claim they have psychic powers. He is well known for challenging Uri Geller’s and Peter Popoff’s powers (video link), Homeopathy healing (video link) and many many more.
I recall seeing a show about James Randi’s offer to pay 1 million dollar to whoever proves the powers of Homeopathy, and judging by the James Randi Educational Foundation website, that prize is still up for grabs.
James Randi is like a modern Mr. Spock. He pursues logical explanations and is willing to challenge anyone who claims to have abilities that negate logic. A very interesting man, to say the least. You can see more videos of James Randi here.