Little Dude is the title one-shot character from the Stanley episode "Little Dog Lost." He is a lost puppy that Stanley and his friends find lost in a bush on a white (snowy) day. Stanley's mother takes him home and then researches about dogs, and teaches some things, like relation to wolves. The puppy calls Harry "mama," much to his dismay, especially seeing as he's a "dude." "Little Dude" ends up being an alias that Harry uses to refer to the puppy.
On the Great Book adventure, he gets lost, but with some help, Harry finds him. As soon as they are out of the book, it turns out Little Dude has an owner in an elderly lady named Mrs. Green (who has previously been calling him "Baby" as a name) and another dog named Tasha, who is his actual mother.