William John Thoms (16 November 1803 – 15 August 1885) was a British writer credited with coining the term "folklore" in the 1840s. Thoms's investigation of folklore and myth led to a later career of debunking longevity myths. Hence, he is the "father of age validation research" to demographers.

Thoms was an antiquary and miscellaneous writer, for many years a clerk in the secretary's office of Chelsea Hospital. He was in 1845 appointed Clerk, and subsequently Deputy Librarian to the House of Lords. He was the founder in 1849 of Notes and Queries, which for some years he also edited.

Among his publications are Early Prose Romances (1827-1828), Lays and Legends (1834), The Book of the Court (1838), Gammer Gurton's Famous Histories (1846), Gammer Gurton's Pleasant Stories (1848). He also edited Stow's London, and was secretary of the Camden Society.

In the 1870s, William Thoms began investigating claims to "ultra-centenarianism." His essays and in particular his book, Human Longevity: Its Facts and Fictions (1879) make William Thoms the "father of age validation research," especially relevant to the topic of supercentenarians.

This article incorporates public domain text from: Cousin, John William (1910). A Short Biographical Dictionary of English Literature. London, J.M. Dent & sons; New York, E.P. Dutton.

Thoms is credited with inventing the word folklore in an 1846 letter to the Athenaeum. He invented this compound word to replace the various other terms used at the time, including "popular antiquities" or "popular literature". He was fond of the works of James Grimm, which he considered remarkable.

Thoms is buried in Brompton Cemetery, London.

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