The Valerians are a humanoid species who sell weapons and substances used to make weapons to the Cardassian Union. During the Occupation of Bajor, the Valerians would supply the occupying forces on Bajor with weapons grade dolamide. Before arriving there, they would visit Fahleena III, Mariah IV and would have the dolamide purified at Ultima Thule.
The Ornathia resistance cell were among the first cells of the Bajoran Resistance to discover that the Valerians were supplying dolamide to the Cardassians. Lenaris Holem was able to plant a bomb aboard a Valerian freighter and destroy it. (ST - Terok Nor novels: Night of the Wolves, Dawn of the Eagles)
In 2369, a Valerian ship docked at Deep Space 9. Kira Nerys wanted to turn them away, as she believed they were still carrying weapons for the Cardassians, although Benjamin Sisko told her she needed proof. After she was affected by the Saltah'na energy spheres, Kira attempted to board the Valerian ship. (DS9 episode: "Dramatis Personae")