Richard Matheson is best known for his novel I Am Legend, which later became both of The Omega Man movies and, more recently, I Am Legend. However, he was active in writing and Hollywood for years and left behind a pretty large corpus of work.
Far and away my favorite, not only of his but of anything, is the Vincent Price/Peter Lorre/Boris Karloff black comedy The Comedy of Terrors (with special guest appearances by Basil Rathbone and Joe E. Brown). Unlike novels, poems, or paintings, movies are a weird, collaborative beast. Everyone contributes to make a movie what it is (or isn't), and I won't deny that the masterful hands of the "triumvirate of horror" helped shape this gem, but Matheson gave them some excellent material to work with.