Orator Fuller Cook Jr. (May 28, 1867 – April 23, 1949) was an American botanist, entomologist, and agronomist, known for his work on cotton and rubber cultivation and for coining the term "speciation" to describe the process by which new species arise from existing ones.

He published almost four hundred books and articles during his career, and was awarded an honorary Doctorate of Science by Syracuse University in 1930.

Cook served as Honorary Assistant Curator of Cryptogamic Collections at the United States National Herbarium from 1898 until 1948.

[4] Cook also studied myriapods (millipedes, centipedes, and relatives), describing over 100 species and producing over 50 publications.

[6][7] Cook was a member of the American Association for the Advancement of Science, American Genetic Association, Botanical Society of America, Association of American Geographers, Washington Academy of Sciences, as well as the Cosmos Club, a private social club of Washington D.C.[2] The standard author abbreviation O.F.Cook is used to indicate this person as the author when citing a botanical name.