The regency of the Golden Empire provided a means through which the government of the Empire, an absolute monarchy, might be maintained if the Sovereign were to be absent from the Empire or incapacitated (but not dead).
Under an edict put into effect by Rin Sakaros in 119 ABY, the Phoenix Prince would become Regent in the event of the Sovereign's incapacity or departure from the Empire. If there was no designated Heir, the most senior Royal Executor would reign as Regent. In either case, the regency would end when the Sovereign retook her duties. During the regency, however, the Regent had all the powers of the Sovereign (unlike a Royal Executor, who on a normal basis lacked some of the Sovereign's greatest authority).
The law was written specifically to cover physical disability, but not mental defect. As such, it allowed continuation of government if the Sovereign was rendered unconscious or comatose, but gave no mechanism for any agency in the government to declare the Sovereign unfit to reign against her will.
Tariun Sakaros reigned (with the title "Prince Regent") usually when he coerced his sister into taking a vacation on Queen's Garden, and after 139 ABY when Rin went to visit their brother Nagarian. The first Regent other than Tariun was his wife, Breek Zagrev, in 156 ABY (as "Princess Regent") when Rin and Tariun went to visit Nagarian together. The longest regency on record occurred in 158 ABY, when Rin went on a quest to recover her telepathic abilities, leaving Breek in command for slightly over seven standard months (Tariun, though present in the Empire, was busy training his brother Nagarian and voluntarily did not take the regency).
A unique case arose in 139 ABY, when both Rin Sakaros and her brother Tariun (then the only Royal Executor) left the Empire to attend the funeral of their father on Nar Shaddaa, well beyond any functional communication with the Empire. In this single instance, Rin appointed a Council of Regents consisting of the Centurions Sorrik, Chindal, and Eskol Kaartinen; Meyrahal, Consul of Iscandar; and Griiz Nesht, Tribune of Mezlagob. The Council had authority to make administrative and military decisions only when it voted unanimously. It was dissolved weeks after its creation when Rin and Tariun returned to the Empire.
In 151 ABY, as part of the 65 Reforms, Rin created the Sovereign's Council. She further directed that, in the event that the Sovereign, the Phoenix Prince, and all Royal Executors were absent from the Empire, the Council would be empowered to act as a Council of Regents until relieved by someone with superior authority.