Cloud Nine was a luxury liner which escaped the Fall of the Twelve Colonies.
When the Cylons attacked the Cyrannus star system, the Cloud Nine, like all civilian ships, was ordered by the Colonial Fleet to freeze in its position while the military counteroffensive was underway. When the counterattack under Admiral Nagala failed and the Fleet was virtually wiped out along with the civilian leadership, newly sworn-in President Laura Roslin ordered these ships to converge near Caprica. Cloud Nine managed to reach this position, despite suffering damage from Cylon raiders which rendered much of the ship uninhabitable. It jumped away to Ragnar along with all other jump-capable ships, and later followed the Battlestar Galactica out of the star system entirely in search of the fabled planet, Earth.
In the weeks following the attack, Cloud Nine was slowly repaired. When these repairs were complete, it became a waystation for civilians travelling between ships in The Fleet, and provided a relaxing atmosphere. It also provided a meeting place for the Quorum of Twelve, with the President remaining based on Colonial One.