Who is Apa from A Step from Heaven and what is their importance?

Apa leaves Korea with his small family to join his sister, Gomo, in America. He goes to America at the request of his wife, Uhmma, because she dreams of a better life for her daughter. Shortly after arriving in America, Uhmma becomes pregnant. Apa decides that the time has come to leave Gomo's home and find a place of their own. Being forced to accept charity from his sister has put a great strain on Apa, and he takes that stress out on his family. He blames Uhmma for the situation they are in and blames her for making things worse by becoming pregnant.