The ambassador from planet Troyius assigned to accompany Elaan, the Dohlman of Elaas, to his homeworld where she would then marry his planet's leader. However, Petri was stabbed en route aboard the U.S.S. Enterprise by the temperamental Dohlman. Part of Petri's assignment was to teach the Dohlman manners so that she would be more acceptable to his leader as a bride of peace.