From SA Mafia Wiki
The Moderator is the most powerful role in the game of mafia. The Moderator can create and destroy entire games, kill any player, replace old ones, or even add new ones if they so desire. They are privy to all the roles the night actions, and can talk to every player out of thread. Typically they are balanced by not getting a vote. Their win condition is to ensure the players have a fun, fair game.
Oftentimes they are paired with a Co-Mod, a servant who does votecounts and interacts with the proles.
It is a difficult role to have, and Moderator victories are uncommon.
See also: Mod.