An author may collaborate with an artist to produce a book (see my previous post on L. Frank Baum and W. W. Denslow). Authors who also draw or paint as amateurs may produce illustrations either skillful enough or charming enough to be used by their publishers (e.g., J. R. R. Tolkien and Arthur Ransome). It's something altogether different, however, when an accomplished artist uses sketches and drawings as part of the process of writing a novel. I'm thinking of Mervyn Peake because I've just been reading his Gormenghast novels.
The fine edition, The Illustrated Gormenghast Trilogy (Abrams, 2011) reproduces all the drawings Peake made while writing. They that range from doodles to energetic sketches to quite finished portraits. Some occur in the manuscript, as the image shown here. Peake must have been exploring his characters and deepening his understanding of them while he drew these funny, searing, haunting pictures. (For more of them, see The cast of Gormenghast at the official website.) Whatever his method, he managed to create in Steerpike a villain as creepy and obsequious as Dickens' Uriah Heap and as brazen as Milton's Satan.
Question: Does anyone know of other writers whose drawings were aids to composition?