Arthur Michell Ransome (18 January 1884 – 3 June 1967) was an English author and journalist. He is best known for writing and illustrating the Swallows and Amazons series of children's books about the school-holiday adventures of children, mostly in the Lake District and the Norfolk Broads. The entire series remains in print, and Swallows and Amazons is the basis for a tourist industry around Windermere and Coniston Water, the two lakes Ransome adapted as his fictional North Country lake.

He also wrote about the literary life of London, and about Russia before, during, and after the revolutions of 1917. His connection with the leaders of the Revolution led to him providing information to the Secret Intelligence Service, while he was also suspected by MI5 of being a Soviet spy. Ransome was educated in Windermere and Rugby. In 1902, he abandoned a chemistry degree to become a publisher's office boy in London. This precarious existence allowed him to practice writing, producing several minor works before Bohemia in London (1907), a study of London's artistic scene and his first significant book. An interest in folklore, together with a desire to escape an unhappy first marriage, led Ransome to St. Petersburg, where he was ideally placed to observe and report on the Russian Revolution. He knew many of the leading Bolsheviks, including Lenin, Radek, Trotsky, and the latter's secretary, Evgenia Petrovna Shelepina.

During the First World War, he worked for the newspaper Daily News and reported directly on the situation in the battlefields and also on the Bolshevik Revolution of 1917. His sympathies for the Russian revolution and protests against Allied intervention led to disputes with MI5, and he was once interrogated and nearly jailed. After returning from Russia, Ransome started working for the daily The Guardian in Manchester. Following a divorce, he remarried Evgenia Shelepina, who came to England to be with him.

Ransome settled in the Lake District, a rural area in northwest England. After refusing the permanent correspondent position at the Guardian, in 1929, he wrote Swallows and Amazons, the first book of the series, which earned him fame and a reputation as one of the best English writers of children's literature. The books are based on the adventures of the Walker siblings: John, Susan, Roger, and Titty (the Swallows) and the Blackett sisters: Nancy and Peggy (the Amazons). Although many real places in the district feature in his books, he also created his geography, blending memories with fantasy and reality. His passion for sailing is reflected in almost all the books: Swallows and Amazons have a sailing boat that they use to explore lakes and discover new lands.