The distinction I make between a fan character and a true original character is, whose world are they in? Yours or someone else's? If you marketed your character, would you face a C&D from a given company? I find that the original characters I love best are the ones whose worlds I have created myself. Your fan character can be totally unique from all the other fan characters in that fandom, or even throughout the internet. But they are still just a fan character. You did not tell their story from scratch. You told it from where it deviated and/or joined up with someone else's story.
I have an original character who is basically a young Scrooge McDuck in human form as far as his design and the basics of his personality are concerned. This was intentional. But he has his own story and is completely unrelated to anything that someone else owns. Thus, while he is inspired by a character belonging to Disney, he is not a Disney character, and thus I can market him if I wish. I cannot say the same about, say, my gypsy character because he is set in the world of Disney's Hunchback of Notre Dame.