Who is Isaac Okonkwo from No Longer at Ease and what is their importance?

Obi Okonkwo's father, Isaac, is a Christian convert and retired catechist. After twenty-five years service to the Church Missionary Society (CMS), he receives a paltry £25 a year, which makes it necessary for him and his aged and infirm wife Hannah to continue farming. Isaac builds the first "zinc" house in Umuofia.