Who is Jacob from Brother Odd and what is their importance?

One of the only adult students at St. Bartholomew's Abbey, Jacob is in his mid twenties and afflicted with a disease similar to Down's Syndrome. A misshapen head and jaw, and one eye lower than the other make his face and head seem somewhat lopsided, but he lacks the flat nose usually characteristic of Down's children. He has a stocky build, a thick neck, and his left temple is convex, while his right temple is concave.