The Highest IQ ever was William James Sidis, with an IQ score of around 250-300. He was an American child prodigy with exceptional mathematical and linguistic abilities and was fluent in multiple languages by the age of six. However, it's important to note that IQ tests have limitations and there is an ongoing debate about their reliability and validity in accurately measuring intelligence. Additionally, there have been instances of people claiming to have higher IQ scores, but their claims are often not independently verified.