Genius is one percent inspiration and ninety-nine percent perspiration.

We traced this famous aphorism through several channels and found it consistently and near-universally credited to Edison, with no serious rival claimant. The strongest documented instance we could verify is chemist M. A. Rosanoff's account in *Harper's Monthly Magazine* (September 1932, p. 425), where he reports asking Edison about genius and quotes the reply: "Genius is one per cent inspiration, ninety-nine per cent perspiration." We also confirmed still earlier press attributions during Edison's own lifetime, including reporting traced back to at least 1903 in the *Ladies' Home Journal*, indicating the wording circulated as Edison's while he was alive; our review of the historical record shows both the "one/ninety-nine" and older "two/ninety-eight" ratios appearing, with the one-percent form crystallizing over time. The book database confirms the line is routinely printed with Edison's name (for example, W. Clement Stone's *Believe and Achieve* and Ross Lovelock's *The One Thing You Need to Know* both attribute it directly to him), but these are downstream repetitions rather than primary evidence. The 1930 *Collier's Weekly* reference cited in one lead we could not independently confirm as a verbatim primary text, so we lean on the well-documented Rosanoff report instead. Under our strict policy this remains an interview report published after Edison's death rather than a text authored by Edison himself, but it is a serious, specific, direct-encounter source and no credible competing origin exists, so the attribution to Edison stands firmly. Verified.