Kellec Ton was a Bajoran doctor who was assigned to Terok Nor in the 2360s by Gul Skrain Dukat, so that he could treat the Bajoran workers.
At some point prior to the 2360s, Ton was married to Starfleet doctor, Katherine Pulaski. While the two were clearly attracted to each other, the marriage soon ended in divorce, but they still remained in sporadic contact with each other. Following the divorce, Ton decided to return to Bajor and set about treating his people, who had been brutalized by their Cardassian oppressors. Ton made his hatred of Cardassians publically known and was known to cultivate links with the Bajoran Resistance, despite this he was tolerated and respected as a doctor.
At some point, Gul Dukat brought Ton aboard Terok Nor so that he could treat the Bajoran workers who were charged with ore processing. While Dukat claimed it was out of a desire to treat his Bajoran workers humanely, Ton saw that it was only to make sure that the workers remained healthy so that his quotas could be met. This led to many tense arguments between Dukat and Ton, but the situation was always calmed by Narat, the Cardassian doctor and go-through for Ton. While aboard the station, he also kept his ties with the Bajoran Resistance, when he would often supply information to local cell leader, Ficen Dobat.
The Double Helix crisis
When the Double Helix virus was brought aboard Terok Nor in early 2366, the station's medical facilities were stretched to breaking point as Cardassian soldiers and Bajoran workers lay dying next to each other. While Ton and Narat were researching together to combat the virus, the Bajorans were left to be treated in the inadequate medical facilities in the Bajoran sector of the station. When Dukat ordered that Ton go to the Cardassian infirmary to work with Narat there, Ton demanded that the Bajoran patients also be treated with the better equipment in the Cardassian infirmary, which Dukat reluctantly agreed to, and eventually Ton requested outside help from his ex-wife, Dr. Pulaski.
When Pulaski and her team eventually arrived on Terok Nor, the three doctors set to work on finding the cure for the disease. With a fresh perspective, Pulaski was able to discover that the Bajoran strain of the virus was also the trigger of the Cardassian strain of the virus. Realising that Dukat and the Cardassians would use this as an excuse to annihilate the Bajorans to stop the spread of the disease in Cardassians, Ton and Pulaski agreed to sit on the information. Eventually, a temporary cure for the disease for patients who already displayed symptoms were developed, however, in twelve hours it was found that those who were cured had reinfected themselves. Eventually, with the help of Bajoran Resistance member, Kira Nerys, the cause of the virus was found, and a permanent cure was developed. (TNG novel: Double Helix: "Vectors").