The claim that Bobby Fisher had an IQ of 187 is dubious and was probably created by an American cold-war era propagandist after his match with Spassky. If you find a book with this claim and check the citations, the paper trail doesn't check out.
There is a common misconception that chess is a measure of intelligence. Bobby Fisher, on the other hand, repeatedly said that chess is a memorisation game. Professional Chess players will autistically study a book of starting moves and memorise the contents. Then they will study a book of mid-game strategies and memorise the contents. Then they will study a book of end-game strategies and memorise the contents. Then, during a game, they will look at the board and recall to memory the moves they read the week before and play that move.
Garry Kasparov was the best chess player in the world from 1985 to 2000. Der Spiegel decided to get him to do an IQ test. He scored 123 on Raven's progressive matrices. About 1 in 20 people have IQ scores above 125. If you get 20 random white people in a room, one of them is smarter than the guy who was Chess Grandmaster for 15 staight years during the 20th century.
