According to wikipedia, The Friendly Ghost, the first Noveltoon to feature Casper, was released by Paramount in 1945, which I guess makes 1962’s Gus Was a Friendly Ghost a little bit of a rip off. However, with the exception of the title, Jane Thayer’s Gus and Casper don’t have too much in common as Gus might have an undiagnosed mental disorder. The plot centers on an old house where Gus lives in the attic. The Scott family lives there part of the year and when Gus rattles chains, they laugh cause they don’t believe in ghosts. When the Scotts take off for the winter Gus is bored and alone. He befriends a mouse and spends his days making the mouse comfortable and happy in the house (can you say co-dependent?)
The story hits its dramatic point when the Scotts come back to the house to enjoy the warm weather. The mouse is very unhappy, but since Gus has a crush on Mrs. Scott he thinks everything will be okay. Of course the mouse isn’t cool with his new limitations in the house and acts out. I won’t spoil the ending but if you know anything about human/poltergeist crushes you can guess who wins. The book has a subtle sixties vibe that you just don’t see that much of these days and no annoying Casper, so check it out.