The Regulators are a faction of orthodox human religion. They formed as a backlash to the book Days of Earthly Walking, which was the story of the True Immortals that helped end the Time of Two Kings.
It was a particularly popular movement among conservative humans who believed that the world was changing too much. The gods were different, the nobility was no more, and things that weren't people were being considered people (like Undead, magical constructs, and Elf)
To fix this problem, they approached it as a societal problem that needed control. To control, they had three branches. The Regulators Spiritual, which were conservative clergy who used only the older texts and taught that the church was the center of life and that the new ways were heretical. The Regulators Political, which were politicians who where trying to pass laws that helped establish Regulator goals and eventually help abolish the Human Republic to bring back the Empire. The last branch was the Regulators Militant who began as groups of armed citizens who were enforcing religious laws, little more than brigands.
The Regulators were becoming a majority, but what pushed them into the limelight was the Destruction of Castle Krag. The Regulators had already been gathering near the city to help "defend" the people against the Steam Fitters Union. When the rift in reality happened, they were already onsite, and were the first to fight back against the aberrations. The work of the Regulators Militant lead by Vlad, were one of the main reasons that the aberrations did not conquer more of the world outside of Castle Krag.
They went from a slim majority to the main political party. In many people's minds, the Regulators represent law and order. The Regulators Militant is the most obvious sign of them. They went from an all volunteer group that supplemented the military to the most religious of the drafted military being pulled from active duty to become Purifiers. Only the most successful and dedicated of the Purifiers become Inquisitors who act as thought and political police through out the Human Republic, trying to root out corruption (as they see it).
The last three Prime Ministers of the Human Republic were all part of the Regulators. Their current candidate Orin III, lost a narrow presidential election to an actual angel, Daggersz. He was running on a "Bring Back the Monarchy" platform. Some of his defeat was placed on vote-rigging in his hometown of Estaher.