Who is Mingo Sheffield from Handling Sin: A Novel and what is their importance?

Mingo is Raleigh's closest friend. Obese and lacking in self-confidence, Mingo is completely thrown by his wife's transformation into a beautiful, shapely woman. Her weight loss leaves him jealous and feeling inadequate, even though his wife loves him. Over the course of the novel, Mingo comes to appreciate himself for the man he is and finds a new lease on life.