Walter Weedon Grossmith (9 June 1854 – 14 June 1919), better known as Weedon Grossmith, was an English writer, painter, actor, and playwright best known as co-author of The Diary of a Nobody (1892) with his brother, music hall comedian and Gilbert and Sullivan star George Grossmith. Weedon Grossmith also illustrated The Diary of a Nobody to much acclaim.
Grossmith trained as a painter, but was unable to make a living in that capacity and went on the stage largely for financial reasons. He was successful as an actor and as an impresario, and wrote several plays. As an actor, he specialised in comedy roles, and his typical characters, harassed and scheming, became so identified with him that the "Weedon Grossmith part" became a regular feature of the theatre of his day.