A nineteenth-century phonologist. He was the basis for the character "Henry Higgins" in George Bernard Shaw's play Pygmalion, which in turn is the basis for the musical My Fair Lady.
Sweet designed an improved version of Alexander Melville Bell's Visible Speech, and his work was also instrumental in the development of the International Phonetic Alphabet and much of later phonology. In fact, if you watch the movie of My Fair Lady, in the scene where Higgins is writing down Eliza Doolittle's speech and he shows her his notebook, the writing there is in Visible Speech (I haven't yet transcribed it).