Jerry was one of the gyptian men on the voyage to the North to rescue the missing children from the Gobblers. He was a stout and placid man with a seagull dæmon named Belisaria. Lyra Belacqua quickly became friends with him after he taught her how to sew. Jerry helped make her a waterproof bag for her alethiometer and also told her why dæmons had to settle.
When Belisaria was growing up, she loved being a porpoise before she went on her first voyage at sea. Being a seagull meant that she and Jerry weren't grand, splendid or beautiful but tough and able to survive by finding a bit of food and company.