The ROK stood for "Rihannsu Opposing s'Khnialmnae", and is a fairly active terrorist organization in the Romulan Star Empire. It's members have infiltrated nearly every organization, and it's network is considerable in size. Even though the Galae and Tal'Shiar are constantly sniffing out embedded ROK members, they are replaced just as quickly.
The ROK has been instrumental in a number of organized attacks against the Rihannsu people, including the near destruction of the ChH Rokhelh'Ael, sabotage of many Galae and RHA vessels, theft of supplies, many assassinations and assassination attempts, and the destruction of many shuttlecraft (more importantly, the personnel aboard at the time).
At one point, the Galae determined that an extremely large force of ROK were based on Hellguard (Thieurrull). The Aen Wing was dispatched with a large amount of ground troops to sniff out the many cells and destroy them. As it turned out, the force was even bigger than imagined, and the Galae was forced to fire-bomb a large portion of the planet in order to reduce the threat. The ROK did most of the damage themselves however, triggering large detonations all over the planet and eliminating the majority of the civilian population. The Empire is still recovering from the 'Hellguard Holocost', and many members of Galae Command are burdened with extreme guilt for forcing the ROK into such a retaliatory act. Living conditions on the planet are minimal, and it is avoided by the majority.
The ROK claim they are only targetting influential s'Khnialmnae personnel, and those that directly support s'Khnialmnae, and were most active when a series of s'Khnialmnae held the position of Daise'Fvillha. A number of ROK attacks have targeted s'Mnhaell'hu as well, since they were the second most powerful hfihar at the time. Some suspect these attacks were staged however, to alleviate suspisions that the ROK were in fact controlled by s'Mnhaell'hu. This has never been confirmed. ROK activities did die off significantly when S'Kurn tr'Mnhaell'hu was appointed as Daise'Fvillha however.