John Olday (10 April 1905 – 1977), birth name Arthur William Oldag, was an artist, cartoonist and writer, and an anarchist revolutionary. He was active in Germany, France and Britain in the 1930s and 1940s and resided in Australia during the 1950s and 1960s. Returning to London in about 1970, he remained active in anarchist groups until his death in 1977.