Here's yet another actor who was happy to dramatically change his appearance for the sake of a single role. You can't say that big-name performers aren't dedicated to their craft! This time it's Charlie Hunnam, looking nothing like we've seen him before or since.
The movie in question was 'Nicholas Nickleby,' and the contract he signed was good enough to persuade him to depart a long way from the chopped, clean look we usually associate with him. That still wouldn't explain the hat, though.