Who is Scimo from History: A Novel and what is their importance?

Scimo is an orphan. He has learned his way around the streets of Rome out of necessity. Useppe and Bella find his hiding place near the river..... a place where all of his treasures are hidden away. Useppe finds Scimo impressive because he's older and goes to the movies. Scimo even escaped from an institution, which is why he's hiding out.