Who screen wrote The African Queen?

I am not sure about the movie, but it was based on a novel by C.S. Forrester who was much better known for his fictional Nelson-Era Captain Horatio Hornblower. by the way a sort of juvenile clone in the Tarzan mode- Tarzan and the Great River dealt with the saga of a steam lighter captain ( Jan Murray) a female doctor ( do not recall her name) and a native youth and of course Tarzan, theatre of operations was the Amazon, but there were surprising similarities in the plot. There was some welcome humor from Captain Bishop ( as he was known in the story) Actor Jan Murray is best known as a comedian, not so with the Bogart. James Agee co wrote the screenplay with the director John Huston, and numerous changes were made from the C.S. Forrester novel.