He is a mystery. A closed book. Not much is known about this mysterious scarlet eyed man in a top hat and tailcoat. He speaks french occasionally to Liddell, calling her beautiful and saying goodbye.
He is a servant to Queen Alice, the Hatter had fought in the Great War along with the Queen. This could mean that he might even be stronger than Loue in battle. The Hatter's tauth doll's fighting skills are extremely potent, even though it does not use any form of magic, unlike Loue.
This man is quite mysterious, but can also be very charming. His odd messages and clues that he leaves for Liddell leave you wondering, 'are they just mad ramblings of nonsense, or do they hide some sort of deeper meaning...?'
In all, even under his questionable madness, the Hatter is indeed a man of mystery.