The Oswaldites were a secret reformist group that existed within the Terran Empire of the Mirror universe. They were formed by Emperor Oswald when Spock travelled back to 20th century Earth as part of his initiative in changing the Empire into a more benevolent force. The impact of this meeting led to a tampering with the tlmeline that brought about the creation of the Oswaldites. Prior to this event, the Oswaldites did not exist in the Mirror universe. Spock also further strengthened the Oswaldites when he travelled to 1986 Terra in order to rescue a pair of Humpback whales when an alien Probe arrived over Earth.
Upon his return to his own time, Spock learnt of the dissident faction of Terrans known as the Oswaldites who were a group targeted by Imperial Security. However, Spock used his position to monitor and protect the Oswaldites from punishment. Eventually, he learnt that the Minister in charge of the Ministry of Vassal Affairs, Samuel T. Cogley, was in fact the leader of the Oswaldites. He intended to use his position to change the Empire from within. Following Cogley's ascension to the post of head of Imperial Security, the Oswaldite movement began to grow in strength which led to openly question the Terran Empire's regime. (Decipher RPG module: Through a Glass, Darkly)