Rettik is a Kazon-Nistrim officer under Maje Culluh who takes the first secret transmissions from Michael Jonas, the Voyager crewman passing information to Seska during the second season.
Rettik is seen in the second-season episodes Alliances and Threshold. He serves the Kazon-Nistrim under First Maje Culluh, and it is to him that Michael Jonas, a disaffected former Maquis in Voyager's engine room, opens a covert channel.
Jonas wants to speak to Seska and offers details of the ship's technology and plans. Rettik is brusque and wary, treating the human as a tool whose usefulness has yet to be proved, and insists that reports go through him.
The thread runs quietly behind several otherwise unrelated stories. In later episodes Jonas deals with another Nistrim, Lorrum, and the betrayal is finally exposed in Investigations, where Jonas dies and Neelix and Paris reveal the scheme.