Carl Barks may not have created Donald Duck's three ever-present nephews, but he sure got the most out of them. Depending on the story, Huey Dewey and Louie functioned as everything from antagonists to Greek chorus. With the creation of the Junior Woodchucks and their all-knowing guidebook, Barks was able to condense a ton of exposition into a very few panels of story (and had a handy source of deux ex machina if he needed it).
My favorites, though, are the stories where the boys match wits with Donald. The power struggles of adult vs. child are familiar territory for everyone; maybe that's why these stories are still so much fun to read.
Here is "Truant Officer Donald" from Walt Disney's Comics & Stories #100 (January 1949); art & story by Carl Barks (the front and back covers are by Walt Kelly):