The late great Stephen Hawking was often cited as one of the smartest men in the world... but when asked what his IQ was, he replied "I have no idea. People who boast about their I.Q. are losers."
Hawking would not have been able to take an IQ test later in life, anyway, as his ALS prevented him from speaking or using his hands, the computer he used to speak took a fair bit of time to say anything, and IQ tests are timed.