Otto Wilhelm Masing (8 November [O.S. 28 October] 1763 in Lohusuu, Kreis Dorpat, Livland Governorate – 15 March [O.S. 3 March] 1832 in Äksi, Livland Governorate) was an early Baltic German Estophile and a major advocate of peasant rights, especially regarding education.
In 1795, Masing compiled and published a children's reading textbook, the ABD. (The letter 'C' does not appear in Estonian words, and back then, was not considered a member of Estonian alphabet. This considered, the title could be translated as "ABC.")
In 1821–1823, Masing published a newsletter Marahva Näddala-Leht (Estonian for Peasant's Weekly), one of the earliest regular publications in Estonian language.
Among other linguistic contributions, Masing is credited with creating the letter 'õ' to denote an Estonian phoneme not found in other nearby languages.