Who is Jonathan from Mrs. Mike the Story of Katherine Mary Flannigan and what is their importance?

Jonathan is the Blackfoot Indian, who Oh-Be-Joyful is in love with. He is not well-liked by the sisters at the Mission because of the sins of his father, who waged war against the Canadian government. Jonathan is desicrbed as proud, tenacious, and stubborn, yet he knows who he is. After Oh-Be-Joyful dies of the flu, Jonathan brings their infant daughter, Kathy, to the Flannigans for informal adoption.