Davis is a character in Greg's book, Stones To Abbigale.
Davis is James, the main character's best friend. Davis greets James every day on the bus by praising him in a over-the-top goofy fashion.
James, Abbi, and Davis witness a man commit suicide over a bridge. Davis runs to help the man, but is killed when he is struck by a car.
Davis is only describes as short in the book.
Greg says he based parts of Davis' story off of his friend from High School. He says his only friend died after High School. (Source)
Greg is most likely talking about his friend Jad.