John Blackthorne is the hero of James Clavell's 1975 novel Shōgun, and is loosely based on the life of the 17th century English navigator William Adams, who was the first Englishman to visit Japan. The character also appears in the 1980 TV miniseries Shōgun, played by Richard Chamberlain.
In the novel, Blackthorne is a described as a navigator, who is the "first English pilot ever to get through Magellan's Pass," working for Dutch traders in 1600 who navigates his ship, the Erasmus, to Japan, where he and the surviving crew are immediately imprisoned. A Protestant like his crewmates, Blackthorne is branded as a heretic by the Portuguese Jesuits who control all foreign trade in Japan, though the Jesuits are powerless to kill him outright due to local political considerations. Blackthorne is taken to Lord Toranaga (also based on an historical figure, Tokugawa Ieyasu), the daimyo in control of the territory in which Blackthorne and the Erasmus first landed. Toranaga quickly realizes that Blackthorne and his ship present a great opportunity, not only in his dealings with the Portuguese, but also in his struggle with his main rival, Lord Ishido (based on Ishida Mitsunari), over future control of all of Japan. Toranaga orders Blackthorne's imprisonment, not to punish Blackthorne, but to keep him out of Ishido's hands. While in prison Blackthorne meets a Franciscan priest who gives him a much greater understanding of the political and economic situation in Japan, and how the Portuguese and the Jesuits fit into it. The priest also begins teaching Blackthorne the rudiments of the Japanese language.
Having been told by the priest that all who enter the prison are eventually executed, Blackthorne is prepared to die when his name is called (like the historical Adams, the Japanese call him "Anjin-san" - Mr. Pilot - because his English name is too difficult to pronounce, there being no sounds or characters in Japanese for much of his name). Instead, the guards take him to Osaka Castle, where he is cleaned up and told by Mariko - the Christian wife of one of Toranaga's samurai who, like Blackthorne, is fluent in Portuguese and Latin - that Lord Toranaga wishes to know more about England and its war against the Spanish and Portuguese.