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.