William James Sidis, American mathematician and anthropologist (b. 1898)
William James Sidis (; April 1, 1898 – July 17, 1944) was an American child prodigy with exceptional mathematical and linguistic skills. He is notable for his 1920 book The Animate and the Inanimate, in which he speculates about the origin of life in the context of thermodynamics.

Sidis was raised in a particular manner by his father, psychiatrist Boris Sidis, who wished his son to be gifted. Sidis first became famous 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. He entered Harvard at age 11 and, as an adult, was claimed to have an extremely high IQ, and to be conversant in about 25 languages and dialects. Some of these claims have not been verified, but many of his contemporaries, including Norbert Wiener, Daniel Frost Comstock and William James, supported the assertion that he was extremely intelligent.