Professor Layton got his hat from his girlfriend, Claire, when he was 27. She gave it to him as a gift for becoming a professor at Gressenheller University. At first, he was unsure about it, but Claire told him that it suited him really well. She died later that same day, so he refuses to take it off out of respect and devotion to her. The hat is a dark brown-black color with a red stripe at the brim.
When Celeste reveals who she really is, she comments on how well he had taken care of the hat since she gave it to him.
Layton has taken his hat off a few times in the first trilogy of games in the series. The first time was in Unwound Future, when Claire returns to the past to die completely. Weeping, he removes his hat in honor of his beloved, revealing his scruffy brown hair. After the credits roll, Layton, after receiving a letter from his apprentice Luke Triton is seen smiling without the hat on. The hat can be seen on the table behind him, although it may have been the spare hat seen earlier in the game.
Layman, a character from Unwound Future, wears a very similar hat.
Layton has a spare hat in his office at the university. It is possible that Layton lent that one to Don Paolo to aid with his disguise in Unwound Future.
It is revealed in Unwound Future that the he wears his hat at all times in memory of his late girlfriend, Claire.
He also seems to have a version in white, which matches the white suit he wears on special occasions.
The Masked Gentleman wears a similar white top hat, although it appears to be slightly less tall.
Prior to receiving this hat from Claire, he wore a red flat cap.
The hat is used as Layton's signature, appearing on his door, as his seal and as the symbol of the game series itself.
In Unwound Future, he is quoted as saying "Is there any greater proof of one's gentlemanly nature than a fine top hat?"