I think it's Saul and that it references this panel from chapter 1000
View attachment 631736
Why it makes this reference, I am not sure. Maybe because they're both D.s?
speaking of which, I just realized that every D in the story wears some headgear
Luffy - yeah okay we know
Roger - originally the strawhat, later a captain's hat
Blackbeard - also a captain's hat
Ace - his laughing/crying hat
Law - leopard hat
Rouge - the flower in her hair
Saul - a stetson hat
Dragon - his hood
Garp - his dog mask and I swear we've seen him wear hats in atleast one casual setting
Lili - we see her wear a crown in the silhouette, despite Cobra and Vivi (who don't carry the initial officially) not wear anything like this
idk if that means something, maybe it's just a reach