Who had or has the highest IQ ever?

While it's challenging to definitively determine who has the highest IQ ever, Marilyn vos Savant, an American author and columnist, was listed in the Guinness Book of World Records for having an IQ of 228. Other notable individuals often mentioned include William James Sidis, who was thought to have an IQ between 250 and 300, though such estimates are speculative. It's important to note that IQ tests can vary widely, and measuring intelligence encompasses more than just a single numerical score.