George Orwell certainly was a successful writer (in the sense that he became famous and sold many books), but not a world-builder. 1984 is a rip-off from Zamyatin's novel, "We".
Ironically, Orwell wrote before WWII that Aldous Huxley's Brave New World (1932) was heavily inspired by We (1921). Then he wrote 1984 (1949) which borrows even more: it's the same story, with more romance and a more mainstream narrating style.
Things like 1984 don't really count as fantasy though (unfortunately) as they were an extrapolation of things that were already happening in the 1930s and 1940s.
