That face says it all, really.
And so does the letter. So when Innocent decided Charlie would be their 'O' and asked us to find an imaginative place to stick it (if you'll pardon the expression - it's a fridge magnet) there wasn't really much competition. 'Oh' is Charlie's immediate response to almost anything involving mischief, mishaps or mistakes. 'Oh' is his answer to the 'look what you've done' question. 'Oh' is what he says if he'd really like to say 'no' but wants to let you down a bit more gently.
So, ladies and gentlemen. I give you Charlie - the 'Innocent' King of O!