Who has 400 IQ?

I'm curious, who in the world is believed to possess an IQ of 400? Such a high score is incredibly rare and would indicate an extraordinary level of intelligence. Are there any notable individuals who have been tested and found to have such an astonishingly high IQ? Or is this more of a hypothetical number, used to emphasize the concept of genius rather than an actual measurement? I'm eager to learn more about this intriguing topic.