The Imperial Ruling Council was the main executive and de facto legislative body of the Galactic Empire. The chief ruling body of the Council was the Imperial Inner Circle, comprised of the Empire's most influential and powerful men, notably the Emperor's closest Advisors.
The Ruling Council was responsible for the every day management of the Imperial government; the Ruling Council created the agenda and passed it on their various subordinates, including the Imperial Moff's Council. The Council was led by the Grand Vizier, the head of government. The Grand Vizier was the de jure second-in-command of the Empire, directly beneath the Emperor. However, the Grand Vizier was overshadowed by the Military Executor and the Emperor's Dark Side Elite.
The Council itself resided in the Imperial chain of command directly beneath the Imperial Commander-in-Chief (the Supreme Commander of the Imperial Forces and the Military Executor) and the Commander-in-Chief's two subordinate councils, the Grand Admiral and Grand General's Council). It did, however, hold authority over the Moff's Council, COMPNOR and lesser divisions of Imperial High Command - and thus, the military and Imperial Intelligence.
Although the Imperial Senate was responsible for legislation officially, it was the Ruling Council that truly held this power. Operating at the Emperor's wishes, the Ruling Council set forth all the Empire's laws and policies, including the Human High Culture agenda.
After Palpatine's death at the Battle of Endor, and the subsequent fragmentation of the Empire, the Ruling Council officially dissolved into the Interim Ruling Council. It would lead the remnants of the Empire from Dreven after the fall of Imperial Center. The Interim Ruling Council would elect a leader to represent the Empire as a de facto Emperor of sorts, but the Council was unable to restore the Empire to any level of efficiency until the advent of Bacharan Valak in 6 ABY. When Valak was coronated Emperor in 8 ABY and the power struggle ended, the Interim Ruling Council was abolished and the Ruling Council was restored to return to its former duties.
The Council would move its official housing to a reclaimed Imperial Center in 15 ABY, where they took back residence in the Imperial Palace. The Imperial Ruling Council publically ended the decades-old agenda of Human High Culture under reforms sponsored by Moff Bailey Laran. However, very little noticeable change has taken place, the highest levels of Imperial Government and the Military are still closed to non-humans that cannot at least pass for Humans.