Who is Old Martin from Fugitive Pieces and what is their importance?

Old Martin is a merchant on Zakynthos Island. He supplies Athos and his ward, Jakob Beer, with essential supplies during World War II. Old Martin had known Athos's late father. One night, Old Martin shows up with his son Ioannis, Ioannis's Jewish wife Allegra, and their young son Avramakis (Match), who are carrying all of their belongings as they flee the Nazi occupation. Athos hides them briefly until they join fellow Jews who are scattering across the island. Ioannis's family moves to Corfu, but they all perish when the Nazis sink their boat. Old Martin does his best to provide food to the Jews during the occupation, becoming known as the "Patron Saint of Groceries". After the war, Martin is gray and arthritic. Sadly, he is dead by the time Jakob returns to Zakynthos.