The prequel of Heart of Darkness is entitled Youth and was published in 1898. (Introduction by Hampson.)
Chinua Achebe, Nigerian author of Things Fall Apart, wrote an infamous criticism entitled "An Image of Africa: Racism in Conrad’s Heart of Darkness," that accused the novel of being racist. Other literary critics have found Achebe’s essay very provocative and controversial; it has spurred a number of heated arguments. (Introduction by Hampson)
Heart of Darkness is largely biographical. Joseph Conrad traveled up the Congo River in 1890 in what was apparently a horrifying journey. And in 1891, he cruised on a British yawl called the Nellie. (Introduction by Hampson)
Though he wrote Heart of Darkness in English, it is Joseph Conrad’s third language, his first two being Polish and French. (Introduction by Hampson)
Heart of Darkness inspired English poet T.S. Eliot to write his cryptic, modernist poem called The Wasteland in 1922.
Apocalypse Now, directed by Francis Ford Coppola is based on Heart of Darkness.(Source)