Augustus Edwin John OM RA (4 January 1878 – 31 October 1961) was a Welsh painter, draughtsman, and etcher. For a short time around 1910, he was an important exponent of Post-Impressionism in the United Kingdom. He was the brother of the acclaimed painter Gwen John.

Although well-known early in the century for his drawings and etchings, the bulk of John's later work consisted of portraits, some of the best of which were of his two wives and his children. He was known for the psychological insight of his portraits, many of which were considered 'cruel' for the truth of the depiction. 

By the 1920s, John was Britain's leading portrait painter. John painted many distinguished contemporaries, including T. E. Lawrence, Thomas Hardy, W. B. Yeats, Aleister Crowley, Lady Gregory, Tallulah Bankhead, George Bernard Shaw, the cellist Guilhermina Suggia, the Marchesa Casati and Elizabeth Bibesco. Perhaps his most famous portrait is of his fellow-countryman, Dylan Thomas, whom he introduced to Caitlin Macnamara, his sometime lover who later became Thomas' wife.