Walter Carruthers Sellar (27 December 1898 – 11 June 1951) was a Scottish humourist best known for the 1930 book 1066 and All That, a tongue-in-cheek guide to "all the history you can remember," co-authored with R. J. Yeatman. He wrote for the magazine Punch.

Sellar was born in Golspie, Sutherland. He won a scholarship to Fettes College, where he was Head Boy in 1917. After briefly serving as a Second Lieutenant in the King's Own Scottish Borderers during World War I, he pursued a degree in modern history at Oriel College, Oxford. This degree was awarded through an aegrotat in 1922. It was at Oriel College that Sellar met Yeatman, marking the beginning of a lasting friendship, which led to their collaborative and celebrated work.