Who is Greg Davis from The Moon Is a Harsh Mistress and what is their importance?

Greg Davis is the second-most senior husband in the Davis Family line marriage and the pastor of Pillar of Fire Repentance Tabernacle in West-Three Community Hall. It holds Wednesday as its Sabbath. Forced to stay out of public after addressing a revolutionary meeting, Wyoming ("Wyoh") Knott takes refuge with the Davises and in due course is baptized in Greg's church. During the revolution, Greg Davis reluctantly leaves the farm to serve as boss drillman for the isolated, newly completed and critically important second catapult. On the eve of Mannie Davis' dangerous mission to Terra, Greg Davis, at a traditional "Family-talk," proposes adding Knott as a new wife. The wedding takes place immediately and Greg allows the bride to sleep with Mannie. As Terran warships approach Luna, Greg Davis is told to prepare "Operation Little David's Sling," and be ready to take over, should the master computer be knocked out. As "Commander of Armed Forces," Greg Davis is a member of Acting Prime Minister Mannie Davis's War Cabinet.