These days, Sir Henry Rider Haggard is best known for his most famous novels, She and King Solomon's Mines. He was, however, a far more prolific and influential author who brought his own experience and perspective to his novels: a late-Colonial administrator who had worked in South Africa at the time of the Zulu Wars and Boer War, and developed some sympathy for local cultures. (See, for instance, his non-fictional commentary Cetywayo and his White Neighbours).
His African-based work grades into a larger body of historical fantasy: epic and readable in general, though some is a little silly in premise. His co-written The World's Desire, for example, brings together Helen of Troy and Odysseus in Biblical Ancient Egypt. You can find many of these lesser-known novels online (see, for instance, Project Gutenberg and Gutenberg Australia - the latter also has his 1926-published autobiography ). There's also an annotated bibliography at Jessica Amanda Salmonson's Violet Books website, which specialises in scholarly material on "Antiquarian Supernatural, Fantasy & Mysterious Literatures, Vintage Westerns, Swashbucklers, & Juveniles". Salmonson makes a strong case for Rider Haggard's influence on the 'Lost Race' genre and other fantasy literature of the later 19th and early 20th century.
This influence continues to the present. For instance, DM Thomas's 1984 Swallow, a novel about a storytelling Olympiad, features one segment that's a bawdy retelling of King Solomon's Mines. (I'm sure it's no coincidence that it also shares a title with Rider Haggard's Swallow: a tale of the great trek). The quintessential Rider Haggard hero, Allan Quatermain, embodies Haggard's colonial sentiments: a hunter and adventurer who is nevertheless aware of his prejudices and, for the genre, sympathetic to the cultures he meets. As Rider Haggard's work developed, Quatermain increasingly encountered the supernatural and mystical. In the final stories, the elderly Quatermain uses a drug, taduki, to explore his past lives in Babylon and the Ice Age.
If you like the genre of Victorian fantastic fiction, I recommend the two-volume graphic novel, The League of Extraordinary Gentlemen by Alan Moore and Kevin O'Neill. Its basic premise is of Wilhemina Murray (from Dracula), Quatermain, Captain Nemo, Mr Hyde and the Invisible Man being brought together as a national crime-fighting team in a technically advanced alternative 19th century.
Moore has melded an encyclopedic knowledge of Victorian literature with iconoclastic creativity to produce a gripping and tightly-allusive 'steampunk' adventure (nearly every frame contains some in-reference). Volume I brings the main characters together, and contains a standalone short story, Allan and the Sundered Veil, that brings the events of the later Quatermain stories round to the starting point of the graphic novel, where he is found in a Cairo opium den by Mina Murray. Volume II is a retelling of HG Wells' War of the Worlds.
If you don't mind spoilers, Jesse Nevins' Notes on League of Extraordinary Gentlemen gives some of the flavour with a frame-by-frame analysis of the many literary allusions. The movie is enjoyable enough, but shares very little with the book except the basic characters. - Ray