Who is Joseph Binbin Mauvant from Mama Lola: A Vodou Priestess in Brooklyn and what is their importance?

The book and the entire story begins with Joseph Binbin Mauvant. In this story, he is seventy-nine years old and living in the rural, mountainous town of Jean Rabel, Haiti. He is known far and wide as a true African, and a natural healer who has no need for the ason, as he has spirits on him at all times. He begins singing one morning, and disappears, they say, back to Africa. He appears in his wife's dreams to inform her where he has gone and not to come looking for him. Before he leaves, he vomits up a small stone which he instructs his granddaughter to ingest. Of course she refuses, though she realizes regretfully later that what he had offered her was his power.