We all have our Donalds
I read a few comments on here where it seemed there was a different interpretation of the Donald character, and even more alarmingly, people posting on the "Donald Kauffman" imdb page asking if he was real!
So I just wanted to give my two cents.
Donald IS Charlie.
They are two facets of the same person.
The real Charlie Kauffman was wrestling with two sides of who he is whilst adapting The Orchid Thief. His solution? To play those opposing inner voices out within the script itself as twin brothers.
Donald represents the positive, easy going, relaxed and confident persona of the real Kauffman who is happy to write to formula and make money and be successful. He is popular and liked. But ultimately there is something shallow about him or how he feels about himself and this kind of work.
Charlie represents the artistic but neurotic persona of the real Kauffman and how he is constantly struggling to attain meaning and self-confidence in his life and work. He wants to create things of beauty and profundity but he lacks self-belief and often turns to the Donald within himself for advice/help.
Notice how the third act of Adaptation is most definitely "written" by the Donald part of Charlie. Car chases, alligators, drug running, shootouts, people overcoming obstacles to succeed in the end, a deus ex machina.
It's like a joke within a joke.
These "twins" are extreme and exaggerated aspects of who the real Kauffman actually is.
Adaptation is post-modern, abstract and inter-textual satire of the very best kind. And the fact Donald has his own imdb page is a testament to how great a movie and script this really was.
We all have our Donald's. Especially those that are writers. Hard to believe this film is over ten years old!