Who is Finn ("Mom") Nielsen from The Moon Is a Harsh Mistress and what is their importance?

The chairman on the fateful night that a "Sons of Revolution" mass meeting is held in Stilyagi Hall, Luna City, Nielsen and Prof. Bernardo de la Paz lock themselves in after the melee with Luna Authority Militia to dispose of all the bodies, and thus heighten the terror of "Yellow Jackets" vanishing without a trace. When he joints the Party, Nielsen's code name is Cornwall. He is initially put in charge of "agitprop," but is soon moved to security. Nielsen at Tube South reports a "Goon" raping and killing all women in Complex, the version that gets enhanced and passed through the cells. Nielsen then leads the attack on the guard barracks and Warden's residence, entering "shoulder to shoulder." Nielsen rises to Speaker of the House but remains an active commander, serving as "Commander of Armed Forces," supervising an 800-man laser gun infantry and, through Knott, all of the paramilitary women's corps. When Prof dies, Nielsen succeeds him as President. allowing Davis to go back to being just a non-attending congressman.