Prax was an officer in the Devore Imperium who assisted Kashyk in hunting down telepaths in 2375. He was very bigoted towards all telepaths, and took part in several inspections of USS Voyager to see if they were transporting telepaths.
He was second in command and when Kashyk defected to Voyager, which was a ruse to locate the telepaths Voyager was transporting, Prax assumed command of the Devore ship. Even though betrayed by Kashyk, Voyager was able to send the telepaths through a wormhole and to safety. Prax wished to have Voyager impounded, and the crew imprisoned, but was overruled by Kashyk, who did not wish a failure to be on his record. (VOY: "Counterpoint")