ORS § 30.610
The actions provided for in ORS 30.510 to 30.640 shall be commenced and prosecuted by the district attorney of the district where the same are triable. When the action is upon the relation of a private party, as allowed in ORS 30.510, the pleadings on behalf of the state shall be signed by the relator as if the relator were the plaintiff, or otherwise as provided in ORCP 17; in all other cases the pleadings shall be signed by the district attorney in like manner or otherwise as provided in ORCP 17. When an action can only be commenced by leave, as provided in ORS 30.580, the leave shall be granted when it appears by affidavit that the acts or omissions specified in that section have been done or suffered by the corporation. When an action is commenced on the information of a private person, as allowed in ORS 30.510, having an interest in the question, such person, for all the purposes of the action, and as to the effect of any judgment that may be given therein, shall be deemed a coplaintiff with the state.
ORS 30.610