Who is Manuel (Mannie) Garcia O'Kelly-Davis from The Moon Is a Harsh Mistress and what is their importance?

The novel's protagonist is also its narrator, Mannie Davis. He recalls events occurring some 70 years earlier, when he is a 32-year old freelance computer technician. A third-generation native-born, free "Loonie," Davis' ancestors are deportees from various parts of Terra and the family tree includes witches, pirates, and terrestrial deportees. The latter explain why he speaks with a distinct Australian accent tinged with Russian words and phrases, and delivered in a clipped style. Before the action of the novel begins, he "opts" into the Davis Family at age 14, is now fifth of nine husbands in a "line marriage" that includes four wives and 17 children, learns various trades from second husband Greg, and studies under Prof. Bernardo de la Paz, but shows little acquaintance with academic subjects like history. He has been to Terra twice for training and hates the planet (particularly North America with its pretending not to be racist). He is not actively religious but shows an acquaintance with Christian scripture. His father lives nearby in Luna, but they are not close.