Borgel is a children's novel written by Daniel Pinkwater. It may well be one of his best. I suppose that it is a science fiction story, but this is Pinkwater, so you don't read it for the 'science', you read it for the wacky.
This is the story of a family who has an old man by the name of Borgel move in with them one day. He claims to be a relative, and why would he say it if it wasn't true? He claims to come from the old country, although he won't say which one. He claims to be 111 years old, and continues to claim this as the years go by. He mostly hides in his room, making occasional evening appearances to pointedly ignore whatever the family happens to be watching on TV. The story starts about a decade after Borgel's initial appearance, when he finally decides to come out of his room and talk to a family member -- the youngest son, Melvin. It turns out that they get along well, and shortly Melvin is helping Borgel hotwire a car to run off to parts unknown, taking only a change of cloths and the family dog. Unknown to Melvin, Borgel is a space-time-other tourist, and has spent the last 900 years exploring the multiverse. Shortly thereafter rich teenagers kidnap Borgel, and Melvin and his dog are stranded at an interglalatic rootbeer stand on a remote offshoot of the interdimensional highway. It gets weirder from there.
It is a wonderful book, somewhat reminiscent of The Hitchhiker's Guide to the Galaxy, but with fewer jokes and better writing. Pinkwater has a very readable and direct writing style, in which he expresses indirect and amusing ideas very cleverly. It is not exactly deep reading, but it is good writing. This being a Pinkwater novel, many sharks are jumped, and with lots of clearance, but he always manages to make it work. I am not a big fan of books that think kids can be entertained by simply escalating the levels of silliness, and Borgel manages to avoid that trap (barely, at times) by having a reasonably coherent metaphysical theory to fall back on, and by having amusing (but not ridiculous) characters.
This is a good introductory book to Pinkwater's longer works, being pretty representative of the style, being a lot of fun, and not being too long or complex. It is much better than his (somewhat unfortunately) popular The Hoboken Chicken Emergency books, and about on par with Yobgorgle and the Snarkout Boys books.
Borgel is currently hard to find as a standalone book, but it was recently republished in the rather large tome 4 Fantastic Novels by Daniel Pinkwater. This book also includes Yobgorgle, The Worms of Kukumlima, and The Snarkout Boys and the Baconburg Horror.