William James Sidis (/ˈsaɪdɪs/; April 1, 1898 – July 17, 1944) was an American child prodigy with exceptional mathematical abilities and a claimed mastery of many languages. After his death, his sister made the unverifiable claim that his IQ was "the very highest that had ever been obtained," but any records of any IQ testing that Sidis actually took have been lost to history. He entered Harvard at age eleven and, as an adult, was claimed to be conversant in over forty languages and dialects. It was later acknowledged, however, that some of the claims made were exaggerations, with a researcher stating "I have been researching the veracity of primary sources of various subjects for about twenty-eight years, and never before have I found a topic so satiated with lies, myths, half-truths, exaggerations, and other forms of misinformation as is in the history behind William Sidis". Sidis became famous first for his precocity and later for his eccentricity and withdrawal from public life. Eventually, he avoided mathematics altogether, writing on other subjects under a number of pseudonyms.