The Rulers of the Universe were a group of elite individuals who controlled events in the universe through computers on their party ship.
Examples of these events were natural disasters such as hurricanes or earthquakes, or economic and political events such as rise and fall of governments. (AUDIO: I Went to a Marvellous Party)
During the early days of the Last Great Time War, the Rulers of the Universe asked for the help of the Eighth Doctor to let them participate in the war. River Song destroyed the party ship, and by extension the group, by planting hundreds of bombs. (AUDIO: The Rulers of the Universe)