Colyus was a holographic figure created by Rurigan, a Yaderan who had lost his friends and village in a Dominion attack.
Colyus, not knowing that he was one of the holograms, served as protector of the village and was investigating the disappearances of twenty-two villagers in 2370. When Jadzia Dax and Odo landed on the planet, Colyus arrested them thinking that they were responsible for the missing people. Odo and Dax eventually helped Colyus solve the mystery. Dax and Odo discovered that all the villagers, except for Rurigan, were holographic projections and that a faulty transformer was responsible for the disappearances.
At first, Colyus did not believe them, but after they convinced him, he persuaded his people that if they wished to continue to exist they must allow Dax and Odo to take them off-line temporarily and repair the reactor before it experienced a complete failure. They agreed and Colyus and the rest of the village were restored. (DS9: "Shadowplay")