Jacob decided to be St. Jerome.
I think the fact that he's learning Latin this year helped in that choice, since St Jerome translated the Bible into Latin.
Jacob's costume was a brown robe which I bought years ago from Oriental Trading. Over top the robe we added a piece of sackcloth with a hole cut into the middle for his head. Little bit of face paint for a beard, a stuffed lion, and I tied a rolled-up brown paper with a feather to his sackcloth shirt.