A Klingon exchange officer aboard the Enterprise caught passing Federation secrets to the Romulans.
J'Ddan is a Klingon officer serving aboard the Enterprise through an exchange program. Using a modified hypospray, he encoded classified schematics into amino acid sequences and smuggled them off the ship to the Romulans.
In The Drumhead, Worf uncovers J'Ddan's espionage after an explosion in engineering raises fears of sabotage. J'Ddan admits to spying but denies causing the explosion, which is later found to be the result of metal fatigue. His confession nonetheless fuels Admiral Norah Satie's widening search for conspirators.