Walter Carruthers Sellar (27 December 1898 – 11 June 1951) was a Scottish humourist who wrote for Punch. He is best known for the 1930 book 1066 and All That, a tongue-in-cheek guide to "all the history you can remember," which he wrote together with R. J. Yeatman.
Sellar was born at Golspie in Sutherland, the descendant of Patrick Sellar who had taken a leading role in the Highland clearances. He won a scholarship to Fettes College where he was Head Boy in 1917. After serving briefly in World War I as a Second Lieutenant in the King's Own Scottish Borderers, he took a degree in modern history at Oriel College, Oxford (which, as recorded in 1066 and All That, was awarded through an aegrotat in 1922). It was at Oriel that he met his contemporary Yeatman, and struck up a lifelong friendship. Although the two produced brilliant work together, they were entirely different personalities: Sellar was somewhat shy and introverted, although he enjoyed acting. He wrote melancholy poetry in addition to dry humour.
On leaving Oriel, Sellar worked as a schoolmaster at his old school Fettes, leaving in 1928 when he moved to Great Marlow in Buckinghamshire in the hope of becoming a full-time writer. However the financial burdens of bringing up two daughters led him to take a job at Canford School in Dorset from the start of the school year in 1929, and he went on to teach at Charterhouse School from 1932 until his death. At first he taught history, but later moved to teach English and he became Housemaster of Daviesites from 1939. He used his own ration and money to buy extra food for the boys of the House during World War II, which made him very popular.