Prester John

Prester John is a 1910 adventure novel by the Scottish author John Buchan. It tells the story of a young Scotsman named David Crawfurd and his adventures in South Africa, where a Zulu uprising under the charismatic black minister John Laputa is tied to the medieval legend of Prester John.
This was Buchan's sixth published novel, but the first to reach a wide readership, establishing him as a writer of fast-paced adventures in exotic locales. He drew the background from his two-year stint in South Africa (1901-1903) as political private secretary to Lord Milner, High Commissioner for Southern Africa, in what came to be known as Milner's Young Men or Milner's Kindergarten. It was in South Africa he gained a feeling for the man of action and the sense of adventure, as well as practical, political training.
A silent film Prester John, based on the novel, released in 1920, was shot and produced in South Africa by African Film Productions. (wikipedia.org)